Students who skipped the associate identifier step

When students accept an assignment on GitHub Classroom they have the option to skip the step associating their username with an identifier from the class roster, but I don’t see how they can go back and complete that step later. Can someone advise how they can do this?

Every time they accept an assignment, they’ll be prompted again to associate themselves with a roster identifier.

Alternatively, the teacher can manually link them in the roster management settings within GitHub Classroom!