I've never done that exactly, although I've had to adjust for foreign work travel. My son also works nights (6pm to 6am) and I've watched him.
I would do a few things:
1. I'd make a plan ahead of time for that weekend after training and before your first night shift. It might make sense to clear any social or other obligations that weekend so you can adjust.
2. I find it easier to stay up later and later rather than go to bed earlier and earlier. So I'd probably try to do something like:
Thursday of training - stay up until midnight.
Friday of training - stay up until 2am
Saturday after training - stay up until 4am
Sunday after training - stay up until 6am
Trying to get a normal X hours of sleep a night (whatever is normal for you).
3. Don't try to switch back to days on the weekends. Just become a permanent night owl. It might be a bit lonely socially because you'll be on an unusual sleep schedule. You can maybe accommodate a bit by having the rest of your wake time be from, say, 4pm to 10pm and hang with people then, or from 6am to noon and hang with people then.
Good luck and congrats on the new job!