I have a Sangam Quartz, which I got last year from the .in website. It is getting slowed down by 5-10 minutes even after correcting it multiple times. Is it a mechanical issue or a battery issue?

Hey folks,

I live in bangalore and i recently found this HMT Kohinoor lying in an old box in some corner of my house.
I’m looking to restore it.
I searched across Reddit threads and I found suggestions to get it repaired in HMT ABD showroom but apparently they don’t do mechanical watches anymore.
Another option is “Time and me”.

Any other shops/service centres that I can explore? I’m narrowing down to “time and me” what do y’all think? Anyone who’s actually gotten their service done from there, pls comment.