All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, you are obliged to sincerely repent to Allaah for stealing the money from the employer. Sincere repentance implies stopping committing this sin again, regretting for having committed it, being determined not to commit it again and giving back the right to its owner. However, it is not a condition to inform the owner of the right when giving back his right to him that you stole the money or that you took it from him, but you should give it back to him in a way that he will be able to get it, like depositing it in his bank account without informing him of the identity of the person who deposited the money.
It should be noted that it is not permissible for an employee to take the money of the employer without his permission even with the intention of giving it back to him because a person who is entrusted to keep the money of someone is not permitted to dispose of it as he wishes except with the permission of its owner.
Allaah Knows best.