bottom bracket clunking noise
First, it may not be your bottom bracket.  Creaks and clunks are notoriously difficult to localize.  If you can reproduce it with the bike on a stand (or upside down on the ground), it may be easier to know for sure.

If it is your bottom bracket, you should replace it (or less commonly, replace only its bearings, depending on the type of bottom bracket).

If you continue to ride, eventually it will probably get worse, but this won't harm anything other than the bottom bracket, so it's not particularly urgent.