Replaced the battery and is it going bad in 8 months

how do you get a hold of ifixit for a warranty issue. Didn’t see anything on there website. Purchased and installed a new battery in a iPhone 6 back in March 2020 and now the phone is charging pretty quick but dies almost as soon as you pull it off charge. Or it will be on charge showing 24% and then you do a couple thing while it’s plugged up and it will just shut down.

thanks

woody