How can I repent and return the money I took from my neighbor's shop, considering that I don't know the exact amount, and the shop owners may not accept it directly from me?

We understand from the question that you used to take goods from a store without paying for them, and the store owner did not ask you for payment out of shyness towards you. If this is the case, what you took is not permissible for you and you must return it. You are not obliged to inform them of what happened; rather, you can devise a way to deliver the money to its owner through indirect means. The important thing is that the rightful claim reaches him. Whoever is unable to ascertain the exact amount of the right due from him is obligated to take precautions to ensure the right of the rightful claimant, by paying him what absolves his liability.