Is it permissible for a chemistry teacher who has become a student counselor to continue receiving the hazard allowance designated for the use of chemical materials? And if it is not permissible, what should he do with the amounts he previously received?

If the entity disbursing the allowance is aware of your transfer to another job and continues to disburse it, then there is no blame upon you for benefiting from it. However, if they are unaware, then you must inform them. If they request its return, then it is obligatory to do so. If they pardon it, then there is no blame. The matter thus depends on the granting entity and the extent of their knowledge.