You can look for alternative solutions to clean your coffee grinder, and you may come across using uncooked rice in some sources. Rice is much harder than coffee and will add extra load to your grinder's motor. It will also become paste-like and stick to areas on your grinder that you don't want. It can also be very challenging to get rid of starch. When rice is mentioned, it may actually be a chemical used to clean mills. Because this chemical combination looks like rice, it is called "rice".
As an alternaive;
Just remove the bowl and wash it. Then remove all rubber parts and top burrs. Then attach the smallest nozzle you have for your vacuum cleaner and suck up all the stale coffee. Extract the coffee residues with your machine in detail from above and below. For any stuck coffee pieces, take a toothpick and loosen it and then suck it out.
For hand grinders with ceramic burrs, separate the parts and wash them in warm soapy water. Wait for it to dry before reinstalling.
For the steel hand grinder, the burrs use the same method as above for the electric grinders.