Two ways, first you must remove the acrylic and product from the bit with a wire brush or by soaking them in acetone and cleaning them. You must sanitize the same way you would your nippers. Nothing less is acceptable and you should always use a sanitized bit on every client. Let them know you are qualified and will not hurt them. You may try introducing the electric file slowly.
Pressure causes friction, and friction causes heat.
Work slower and apply less pressure and be sure to habitually pick your bit up off the nails to cool it as you work. Working from the right to left side of the nail and picking the bit up to go back to the right side will help alleviate heat, going back and forth and never picking the bit up can cause heat. Using an electric filing oil helps with slippage and can keep the nail cooler. Try using a pencil to draw a line to follow. Cut three sections each side and the center.