Need solution to remove mud from borewell

Our borewell is 840 ft deep with the first water source at 480 ft depth and second at 830 ft 2 inch depth. While scanning we found mud filled at 810 feet onwards and water level stored till 630 ft.

Please suggest ways to clean the mud ? How much will the cleaning cost? Will cleaning the borewell be useful? After cleaning, which capacity motor and at what depth, should be installed to pump water?