I am come to Sharjah tourist visa I have overstay...

You can reduce the fine if you are leaving the UAE, and you can request a 50% reduction in exchange for a ban from entering the UAE for a year. If you want to modify your residency status by converting the visa from a visit visa to work visa, in that case you must pay the full fine, and it will not be reduced. Also, the public administration of residence is the entity to which you can apply for a reduction of the residence fine if there is justification for that.