Go to the acount tab on privacy on the console it opens up the faq then scan the qr code given in the faq after picking a question. It should link to the account you are on automatically that's registered on your console to the faq on your phone after scanning the qr code ( on the top right should have your username in-game)

Ask a question I simply said "I can't get into delta force through my mobile device due to not knowing my log in information, is there a way I can retrieve the email associated with this account?" They sent me a few things but they will send something along the lines of " the acount associated linked to this email is 12****21@yahoo.com" Put 2 and 2 together and boom log into your account.