To remove banana stains from a carpet follow the steps detailed below

Make a mild detergent solutions and pour it onto the stain. Then blot
Then apply some luke warm water and blot again. As you are doing this you need to soak up as much of the fluid that is being created. Use some towels or tissue to soak it up.

To remove banana stains from fabric or clothes then have a look at the following

Wash the item in the hottest wash that the item can bear. Avoid using soap as that can set the stain. You can also soak the item in warm water with a little enzyme prewash stain remover for about half an hour. If the stain is really old then you may have to use a mild laundry bleach, If your garment allows it.