The host of a Zoom meeting can turn on the closed captioning option and can assign this role to a participant. If you have been assigned this role, you will see a Closed Caption icon in the video controls at the bottom of your meeting window.

The link below will take you to the vendor's help documentation; you'll find a link to Entering Closed Captions as a Participant in the Overview section. (The vendor's site prevents us from linking to them directly.)

The vendor's closed captioning help page can be found at
https://support.zoom.us/hc/en-us/articles/207279736-Getting-Started-with-Closed-Captioning

The following video from the Zoom Learning Center gives an overview of Accessibility features in Zoom.