Hello I just bought appleconnect account from this user

 

The account seems working fine but I have to login with a pin sent to his number everytime and he says all his clients login that way. Just the day before today I could not login because he was offline only to get pin today and login and find out actually yesterday there were some unlocks done on the same account. Since I have all controls when I'm logged in , is there an expert here or someone with experience on using apple accounts and assist me if i can actually add my number when I'm full logged in as a secondary number before i fully pay for the account?
I was actually given a go ahead i can add a number but i dont see where actually. If have experience please I'm willing to pay and you connect to my team viewer and help. Willing to pay $100 for anyone do that to me.
Thank you