How can one absolve oneself from the salary earned over years of repeated unauthorized absences from work, with the desire to calculate the hours missed or donate their value?

Your departure from work in the middle of working hours without permission is impermissible, and the employer has the right to deduct the duration of your absence. You must repent and adhere to the terms of the contract, for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." As for what has passed, you must seek forgiveness from the officials; if they forgive you, then all is well. Otherwise, you must return the portion of the salary that corresponds to those times to the employer. You can calculate the amount by dividing the salary by the number of days, then dividing the daily wage by two. You should act based on your best estimate if you are unable to calculate precisely.