How does claiming credit for exchange work? Does it happen automatically or do you have to apply for it for each subject you take or?
Depending on the program that you did overseas it's either really complicated or really easy.
Basically, you need to take "equivalent" subjects. For languages, that's really easy - just go and take a course/program and for every 50 hours of time commitment in class you get a subject credit. For other subjects, it might be different compared to simply time - you might need to make sure you cover subjects where the fundamentals for future subjects are also covered; basically getting credits crossed for very similar subjects.
As for the process of doing so, normally what happens is you will plan four subjects and then go overseas and live in another university system for a bit. Meanwhile back at home, UoM gives you a "placeholder" subject worth 50 points = 4 subjects. When you come back, you bring your transcript and hand it to your faculty (I know this is at least true for arts or sciences). After that, you just show the transcript to the person who approved your overseas subjects in the first place. They sign off, send an email to the exchange coordinator, and you get credits.