there is a small flap near the bottom of the machine. Modern machines just a a slit that is minimally wider where you can insert a screwdriver to open it. Sometimes the mechanism is different.

Behind the screws and lids and stuff is a sieve you need to clean. If you see a tube on the side before reaching the sieve, open it firstand let the water run out (careful, can be quite a bit of water) If you have a toploader the cover and sieve is sometimes on top to the side.

You can check your manual if you don’t find it or are unsure how to open.

Sometimes socks, jewelry or other stuff gets trapped in there and can not be chemically cleaned away.