The item's magic is gone for a week, there's not really a remedy.
Your GM might allow a Wish ritual to do it.
Yeah, short answer is "suck it up butter cup".
Other than just purchasing new armor there's nothing to be done.
Depending on exactly what armor it is, you could maybe take off the temporarily un-magic'd runes off the armor and replace them. Putting on temporary +2 potency and resilient runes on the armor should be cheap enough to do temporarily. I assume the armor has +3 runes on, but straight replacing them might be too expensive. But being down by 1, while not great can be survivable.
My thought here is that "normal" armor is not itself magical. It's the runes you put on your full plate that make it magical. Take the runes off and put new on, and you've got functional magic armor again.
Worse case, buy replacement armor with +2 fundamental runes on it and get back to work.
Things you can do.
1) Take a vacation or slow boat trip for a week.
2) Visit a outer plane where time flows faster.
3) Take a week to visit your mother, you don't call, you don't write...
4) Use Mystic Armor spell for a week.
5) Travel a week into the past and take the slow way back to the current present work on your knitting while you wait.
I would allow the spellcaster of the group to try to restore it by magical experimentation in a lab. A wizard could use arcana (Difficulty: Legendary) for example with a DC of the original effect. On a critical fail, I would extend the duration by 1-3 days. I would let them try with only master level in the skill but extend the duration by 1 week on a crit fail instead.