"hijack your post"😆
What version of Moodle are you using? Are there particular students unable to see the recorder? (RecordRTC will not work with macOS /Safari)
I'm using v 3.9. From Moodle 3.5 the default Atto text editor uses the RecordRTC audio recorder
In 3.9 :
Site administration > Plugins > Text editors > Atto HTML editor > RecordRTC
There is a note about capabilities which can control access to the buttons to particular users in particular contexts.
If you have assigned Roles, this may be at the root of your issue. However, I've not experienced an instance where that has been an issue.
Hope this helps...
Kirk