One overwatering shouldn't damage your plant if you have it in a pot with drainage holes and decent potting mix. Just don't water again until the soil feels dry...poke your finger down in and check.

When you have left it to drain on a flat surface for a while, before you put it back on its saucer - tilt the pot to let even more water escape - unless your pot has only one central hole.

If you put some pebbles in the bottom of the saucer - half to one inch across for each - and place the pot on top of them - there will be improved drainage, plus better air circulation for the roots.

So long as you don't have a small plant in a big pot (also known as 'over potting') then the mixture should dry out quite quickly.

So long as the plant wasn't desperately dry before you watered, when its roots would have withered and be ready to rot, then one solid soaking won't cause disaster, as morz8 says.