What is the ruling on the financial increment that will be added to my salary after I obtain a certificate with assistance in one of its subjects, knowing that this assistance occurred without my request, but with my implicit approval, and my original desire was to obtain the certificate through my own efforts?

What the teacher did by helping you solve the questions for that subject is considered forbidden cheating, and you must seek Allah's forgiveness, regret your action, and resolve not to return to it.

As for benefiting from the certificate, there is no harm in that, as long as your field of work has no connection to the subject in which you cheated. Sheikh Ibn Uthaymeen, may Allah have mercy on him, issued a fatwa permitting this if the person repents sincerely and the subject in which he cheated is not related to the work he performs.