How do I find my old Google account user name and password that was synced to my samsung s7

[johnsteal]

I bought my mum a samsung s7 and she seems to forget her old user name and password that was synced to the phone when she created it but now she can't use it unless she gets the old user name and password

 

[bignastyid]

http://www.tomsguide.com/forum/id-2317968/read-passwords-lock-codes-pin-numbers.html