When you’re in the meeting you need to go to the Participants icon like you see below in red, then to the three dot menu and ‘Manage Permissions’
At this point a page will pop up in a web browser, from there you need to change ‘Who Can Present’ from ‘Everyone’ to ‘Only Me’.
This will stop students having the ability to mute your mic.
You may also find other useful settings in there for your meetings 😊.