Reposting my experience with GAT from another thread. You need to cancel the old reservations and get new ones linked to the new tickets. Hopefully your old tickets disappeared as they did for me...
Update on my solution from Get Away Today
*Note they report the deadline for re-issuing tickets is April 29th (that's Disney's deadline, not theirs)
I traded in my old 4-day Parkhoppers with Maxpass purchased Feb 2020. They issued me new stock, 5-day Parkhoppers. Because of the amount I paid for Maxpass, the new tickets were slightly less which they are crediting.
I was worried about the risk of having old/cancelled tickets with Park Passes linked to my account and a lengthy Disney call/chat to fix this. But I really wanted to avoid a trip to the ticket booths (for possible MP refund) which I am picturing being a real mess; especially if they have launched a new membership program before our trip. I also wanted to add a day, and obviously worried about not having Park Pass availability to add a day during our trip.
I'm happy to report success on all. It went like this:
1) GAT cancelled/reissued tickets in just seconds. Clearly it was just a few clicks on their end.
2) In just the time it took to end the call, I went to the App and the old tickets disappeared (sweet, no de-link call to Disney).
3) I went to Disneyland.com and my 4-day Park Passes were still there. I cancelled all... no errors even though the associated tickets were gone.
4) My GAT emails arrived in under 60 seconds (cancellation and new tickets/invoice)
5) I linked the new tickets and booked all Park Passes with no issues (using hotel bucket/VGC)
Happy camper here and I'm a big fan of GAT. Also, score one for Disney IT/ticket system, even though it's a little goofy seeing different things in App/website. At least the database is working. Hope the front end is synched up soon.
Now, if we have issues at the gate or trying to get ROTR Boarding Groups, I will eat my words. But really, everything looks in order. It was a pleasant surprise!
https://www.disboards.com/threads/previously-purchased-tickets-with-maxpass.3834505/post-62917300