So, how do you fix the problem of the voice change?
You don't. You wait for Microsoft to fix it.
There are a plethora of threads about this in the past few days. You cannot get a different voice until Microsoft fixes this.
It is apparently a bug that is for all devices introduced with a recent update.
Writing here does not bring it to the attention of anyone who can do anything about it.
You are addressing your fellow users here.
Microsoft is aware of the problem, though. They are working to fix it. Of course it popped up over a weekend!
I recommend using the Public Feedback Portal.
https://feedbackportal.microsoft.com/feedback/forum/fb6d67e3-301c-ec11-b6e7-0022481f8472
Then, once your feedback is posted, copy the URL and then come back here and post it so that others can comment and vote.
Be the squeaky wheel. Keep pressure on.
You can search for and vote on other feedback already posted. I would suggest a search for "read aloud."
Here is a list of some feedback links:
Feel free to vote and vent a little.
For more on using feedback, see my article: This is a user-to-user support forum. -- You can give feedback TO MICROSOFT designers and decision makers on Microsoft Word or other Microsoft Products using their feedback mechanisms, (not here). (This is a link to directions.)