Concensus is that once they've gotten wet, it is a bear to resweat them. But, if you take them apart, wipe off the solder (and that can be a pain in the fitting), reflux and resolder, you should be okay. If you bang the fitting on a hard surface while the solder is still molten after you separate it from the pipe, you'll get much of it out. It is probably easier to just use a new one. Why do you need to take it apart? Hopefully, you won't have any leaks and leave it alone. The biggest key is to ensure you get the pieces very clean, flux well, heat the fitting, and don't hit the solder with the flame - add it opposite the flame, or after removing it, depending on the size of the fittings.