Re: "I need to change the way certain words and names are pronounced by speak selection in spoken Content,
how do I do that?
For a Mac using MacOS "Big Sur" 11.7:
With pronunciation for spoken content, seems it may be worth experimenting with the array of different voices available, as some may work better for your work-situation than others.
Eg: See Apple Support's online article below:
For MacOS 11 "Big Sur" Change the voice your Mac uses to speak text - Apple Support
__________________________________________________
Re: "I can't find the place in settings where I can do that".
Seems there are no options for adjusting pronunciation of Spoken Content in earlier versions of MacOS.
However there are options when using the newest MacOS 15 Sequoia version if you have access to that.
(Please note: Also options if using "VoiceOver" instead : ie: more details right at the bottom)
ie: For MacOS 15 Sequoia: Change the voice your Mac uses to speak text - Apple Support
Eg says:
"You can change the voice your Mac uses to speak text that’s on the screen,
or
adjust how the voice sounds and how it pronounces certain words."
And to:
"Adjust how a voice sounds
- On your Mac, choose Apple menu
> System Settings, then click Accessibility 
in the sidebar. (You may need to scroll down.) - Click Spoken Content.
- Do any of the following:
- Adjust the sound of the voice: Click
next to “System voice”, then adjust settings for the voice, such as how fast or loud it speaks. Click 
to hear a sample. - Adjust how the voice pronounces certain words: Turn on Pronunciations, then click to define a custom pronunciation. You can dictate or spell out how you want the word to be spoken."
_______________________________________________________
Re: if there is a way that I can do/fix this, then how do I do that?
Those who use "VoiceOver" instead of " Spoken Content > Speak Selection" to speak content have options for pronunciation. However VoiceOver — the screen reader built into macOS — may present quite a learning-curve in order to become familiar with using it.
Eg: For MacOS Big Sur 11: See how to: Use VoiceOver to read text on Mac - Apple Support
and to:
______ _________ Use VoiceOver to hear what you type on Mac - Apple Support
For pronunciation:
See: Pronunciation, Speech category, VoiceOver Utility on Mac - Apple Support
and
You can: Change how VoiceOver pronounces text and symbols on Mac - Apple Support
