Summarize the following:
The buildup of gunk on strainers and stoppers often causes slow drainage. Remove any screws around the strainer with the proper screwdriver. Then, place the screws in a safe location while you clean the strainer. Stopper are easier to remove because they are not held down with any screws, so simply remove the stopper by twisting and lifting it.  Most bathtub drains have either a strainer or a stopper. This method is usually effective on small clogs, so if your drain is badly clogged, it may not be as effective. A lot of gunk may have accumulated on the strainer or stopper. Clean any hair or soap scum; you may have to scrub the strainer and stopper. Strainers will need to be re-screwed back onto the top of the drain, whereas you can just place the stopper back in the drain. Turn on your bathtub to see if the drain now works properly. If not, you will need to try another method.

Summary:
Remove the strainer. Clean excessive gunk around the strainer and stopper. Replace the cover or stopper the same way you removed it. See if it worked.