how to deauthorize all after WIN 10 UPGRADE ***IF*** I ALREADY DID in 1 year.

I hope you are doing well. 😉 I upgraded to windows 10 and now NEED to AUTHORIZE again in ITUNES as I cannot sync /transfer purchases backup correctly

. I already deauthorize all within the 1 year period. BUT NEED IT AGAIN. Actually my IPhone 6 seems to be having a battery issue, it powers down being at 40-50% and I cannot backup to take it to service because I cannot authorize my windows 10 pc. Must deauthorize all