The device itself has no standard voice to text application. There should be an application called "Sayboard" however on the phone. This is what you need to setup and use.
If it is not on the phone for some reason, you can find it and download it in F-Droid.
Once loaded you will be able to access it via 1 of 2 different methods depending on the app you have open.
OPTION 1 (for browser and basically everything but the text messaging app):
click on the keyboard icon on very bottom right,,. like right above this ^
Select "Sayboard" and it will bring up something like the below:
OPTION 2
Inside your text messaging app, if you've set Sayboard as the default keyboard, it will show up as the below:
You simply click on the microphone icon on the top right of the keyboard and follow the same prompts.
Hopefully this helps?
If not there's another voice to text app worth trying that was recently released by a great team out of Austin Texas --> https://voiceinput.futo.org/