How do I fix mixed line endings in SSMS?

I have no idea how this happens, but in SSMS (version 21) occasionally the line endings go wrong. I’m teaching online to users with Windows and SSMS and suddenly they get errors with the GO keyword. This is apparently due to the fact the line endings have got mixed and there isn’t the proper CRLF line ending around the GO keyword. This is with new files created in SSMS on Windows, so I don’t see where the other line endings are coming from. More importantly, I can’t find a simple way of fixing these line endings. I can open the file in another text editor, such as Pulsar, and fix it that way, but I can’t ask the students to do that; besides, there must be a way within SSMS to do this.