The tub drain can be removed using a screwdriver and pliers. If you have time, run down to the home center or hardware store to buy a tub drain remover tool. Carefully turn out the drain counterclockwise, then set it aside. A clay-like substance called plumber’s putty should be placed under the tub drain before you turn it back into place. Without this putty, the tub will leak. So, be patient with this step and make sure that there are no gaps between the putty and the tub.
It is best to roll the putty out into 3/8-inch rope-like pieces and press them onto the tub around the drain hole. Replace the drain, tighten it, and wipe excess putty with your finger. Some drains will have a lever operated plug. This usually lifts right out. The rubber gasket can be replaced if the tub is not holding water well.
Source: The Spruce