Speech to text requires a SAPI speech-to-text engine to be installed on your computer. Most Windows machines already have it installed. You can also install software such as Dragon Naturally Speaking or any other engine which claims SAPI compliance.
Speech Recognition is slow and takes some time. Test it with a short file first.
We recommend you use a work-ahead system (ie. proof one file while waiting for speech-to-text of another).
For information on setting up Speech to Text, please follow the directions in https://www.nch.com.au/scribe/kb/657.html