Follow the below steps to know how to get subtitles in Chromecast.
Step 1: To begin with, disconnect your Chromecast dongle from your TV so that it is no longer linked to your tablet or phone.
Step 2: Next, go to the accessibility settings of your device. On both iOS and Android devices, this submenu must contain caption settings or subtitle settings.
Step 3: Once you make the alterations you need, connect the dongle again to your TV, then launch the Prime Video app again.