I have a technique which I can demo for you which would allow you to set focus on a training course and then it would pop up a list of all your employees using a traditional quick base report which includes dynamic filters and the search box.
Then you would click click click on as many employees as you like and they would be quietly assigned to that course.
Then you would click a button to get back to your course and see a list of those employee training assignments.
Feel free to contact me via my website and and I will give you a demo. QuickBaseCoach.com
It typically takes about two hours of consulting time to set this up for a client and then they can use that technique on their own going forward. The technique does not involve any script, just URL formulas, so it is still in the genre of low code no code.