best bet is to take it out of the tank, and pick the bubbles off outside of the water, then swish it around really good in some tank water in a seperate container before returning it to the tank. Those bubbles (valoina) will contain little baby bubbles/spores that can be released if the bubbles are popped in the tank. If you can keep them out all together you are much more likely to avoid them spreading around the tank.
Another trick is to use a syringe to suck the fluid out of the bubbles before removing them, but in your case IMO removing the clam and cleaning it off outside of the tank would be much safer and easier.