If you want credit for the seminar as a MSc course, you must register on Academia (also if you are a Bachelors student)
If you want credit for presenting your MSc thesis work (as opposed to seminar project), then please only register formally in your final semester
If you want credit for the seminar as a Bachelors course, you should register on KSL
If you need credit for a Proseminar (part of the Bachelors project), then you do not need to register. The grade will be filled in on the Bachelorarbeit in Informatik form.
SCG