The most straightforward answer I can give you is: have them gain less wealth during the next encounters, until you reach the intended balance. In games where XP and money (or their equivalents) are independent, it's fairly easy. The PCs are now overequipped and some higher level fights should be easier for them. Choose enemies that work fine with close to no equipment. Hev the level catch up to the wealth. This works really poorly if you don't want them to level faster for a while. Drop some item now and then, just to keep your players content. Getting treasure is fun.