Most modern hearing aids automatically adjust the volume based on your environment.
But if you'd like to adjust the volume manually, you can do the following for behind-the-ear and in-the-ear hearing aids:
Behind-the-ear hearing aids: The volume can easily be adjusted by pushing a button on the back of the hearing aid. The exact adjustment instructions will vary depending on your hearing aid model, so read your device’s instructions for more details.
In-the-ear hearing aids: Remove the hearing aid from inside your ear and find the volume button to adjust the volume.
Some hearing aids are supported by a phone app which you can use to adjust your hearing aid volume.