How can a person absolve himself of 40 dinars he fraudulently took from medical insurance provided by his workplace, and is it permissible to give this amount to his mother to absolve himself?

It is not permissible to resort to deception and take the excess amount. It must be returned to the insurance company. If you are unable to do so, then donate it to the poor and needy, including a poor, needy mother, provided that you are unable to return the amount to the entity from which it was taken unlawfully.