Take off the cover of the seal, turn it upside down, then carefully drop the ink on the surface of the seal, not too much, just cover the surface, then turn it upside down (the surface of the seal is horizontal and the words are upside down) and let it seep down slowly.

It should be noted that there is a special kind of ink. The general company will provide you with a bottle of ink. If you don't take it, you can buy it from Zhang company (monopoly).