What is the ruling on bribery to enter a health specialization, knowing that the questioner studied and struggled and regrets his action?

Bribery is the act of giving money to establish falsehood or invalidate truth. It is forbidden in Islamic law. The Messenger of Allah, peace and blessings be upon him, cursed the one who gives bribes and the one who takes them. As for what is given to establish truth or invalidate falsehood, it is not considered a bribe for the giver, though it is a bribe for the taker because he consumed money unjustly. If you paid money to obtain a certificate you do not deserve, it is a forbidden bribe. Your regret over it is part of your repentance, so resolve not to return to it and seek Allah's forgiveness. As for working with this certificate, if you perform your work perfectly, there is no harm in remaining and benefiting from the salary. Sheikh Ibn Baz issued a fatwa permitting this, along with repentance for the previous deception.