How to assign an additional/extra/second user-role to multiple users (of a specific user-role)

I have 500 users with 50 of those users assigned to user-role XYZ. I’d like these 50 XYZ users to keep their current XYZ user-role but also be assigned another/additional/extra/second user-role ABC… as a bulk job.

I’m looking for a function that could

1. find all users with user-role XYZ
2. then assign them to a second user-role of ABC