This transcipt function is not available to everyone for the moment and not relased yet. You had to ask to take part of this beta test functionnality. Don't know if you still can. Adobe member may reply to you about it.
De rien 🙂
As Richard says, the transcription/speech to text function is still in Beta. You can apply for access. Here is the FAQ with a link to the request:
Questions and comments about transcription should be posted in teh public Beta forum: