How strange. There must be something quite fragile in the meter.
Sorry to hear a good deed and trying to help someone has resulted in a non working multimeter.
I suggest doing a follow up video.
Taking apart a multimeter shouldn't kill it. I recently worked on a Fluke 77 III, with
no regard to ESD handling, and I must have taken the thing apart at least 30 times (including the lcd with self tappers), washed it 3 times with IPA, and soldered the pcb and it survived no problem.
The problem with "warranty" now is the potentially high shipping costs and long delay back to the seller.
PS. Am I the only one who thinks that the multimeter should read 0.000 when it is on DCV with no input? Virtually every multimeter I have used shows 0.000 on DCV. Even on DC mV, it will settle close to 0.0 given enough time.