A method, performed by a hub device, of storing a voice assistant model for controlling a device, the method comprising: receiving device information of a new device connected to the hub device, wherein the new device is logged in by a user account of the hub device and newly registered in an Internet of Things, loT, server by the user account; after receiving the device information of the new device, requesting, by the hub device, a voice assistant server to update a device determination model stored in the hub device, wherein the device determination model determines a device from among a plurality of devices that are registered according to the user account of the hub device for performing an operation based on the voice input of a user; receiving the updated device determination model from the voice assistant server and storing the received updated device determination model; requesting, by the hub device, the voice assistant server to transmit information about a function determination model corresponding to the new device, wherein the information about the function determination model includes at least one of capacity information of a file constituting the function determination model corresponding to the new device, RAM occupancy information used to read the function determination model, or information about a simulated processing time required for the processor of the hub device for obtaining operation information by reading the function determination model; receiving the information about the function determination model corresponding to the new device from the voice assistant server; monitoring at least one of an average processing speed of the processor, a residual capacity of the memory, and an average RAM residual capacity of the hub device; determining whether to store the function determination model in memory of the hub device by comparing monitoring result information with the received information about the function determination model corresponding to the new device; based on the function determination model being determined to be stored in the hub device, storing, in the memory of the hub device, the function determination model corresponding to the new device; selecting at least one hub device candidate other than the current hub device from among a plurality of devices pre-registered in the IoT server according to the user account logged into the hub device; selecting one device from among the least one hub device candidate based on use history information and performance information of each of the at least one hub device candidate; and changing the hub device by replacing the current hub device with the selected one device from among the at least one hub device candidate. receiving device information of a new device connected to the hub device, wherein the new device is logged in by a user account of the hub device and newly registered in an Internet of Things, loT, server by the user account; after receiving the device information of the new device, requesting, by the hub device, a voice assistant server to update a device determination model stored in the hub device, wherein the device determination model determines a device from among a plurality of devices that are registered according to the user account of the hub device for performing an operation based on the voice input of a user; receiving the updated device determination model from the voice assistant server and storing the received updated device determination model; requesting, by the hub device, the voice assistant server to transmit information about a function determination model corresponding to the new device, wherein the information about the function determination model includes at least one of capacity information of a file constituting the function determination model corresponding to the new device, RAM occupancy information used to read the function determination model, or information about a simulated processing time required for the processor of the hub device for obtaining operation information by reading the function determination model; receiving the information about the function determination model corresponding to the new device from the voice assistant server; monitoring at least one of an average processing speed of the processor, a residual capacity of the memory, and an average RAM residual capacity of the hub device; determining whether to store the function determination model in memory of the hub device by comparing monitoring result information with the received information about the function determination model corresponding to the new device; based on the function determination model being determined to be stored in the hub device, storing, in the memory of the hub device, the function determination model corresponding to the new device; selecting at least one hub device candidate other than the current hub device from among a plurality of devices pre-registered in the IoT server according to the user account logged into the hub device; selecting one device from among the least one hub device candidate based on use history information and performance information of each of the at least one hub device candidate; and changing the hub device by replacing the current hub device with the selected one device from among the at least one hub device candidate.