How do know it's slipped? By how much as something may have got damaged?
To re-align (I would put on a new belt) just pin everthing as above. If the belt has slipped you will need to move the offending pulley until pins go in.
I've been waiting for some warmer weather before doing my cambelt, only done 50k miles but now approaching 10 years old so thought I'd get it done before we're allowed to travel again.
This thread has a lot of useful info so thought I'd add something (see attached) that I found on Service Box about the crankshaft bolt. It seems there's a danger of twisting the bolt due to the threadlock jamming if you don't take care, for this reason an impact wrench is not recommended. I've not read any stories about this happening but I'm guessing it has or PSA would not document it.