How to log into the gmail account for the account I bought?

Seller: DyonisXX

We're trying to trade an account that uses Gmail/Google as log in but whenever I try to log in it tells me to recover the account and when I try to recover it, it tells me that there's not enough info and that it either needs the same IP or the same device. How do we fix this? Edit: OH **** He linked his phone and that allowed to me log in but the moment I changed the password the account got locked, how do I fix it?