You have a choice of a longer spindle or a spacer, with the best or possible option depending on the specifics.
If you have a classic cup/spindle BB, you can add a spacer under the right cup, but you'll be limited because the left cup get recessed the same amount and there may not be enough for the lockring. So a longer soindle is the best answer if you need more than 1-2mm max.
OTOH if you have a cartridge BB that doesn't use lockrings, than a spacer behind the right cup is simple and all you need.
Modern external BBs may allow you to solve it by switching spindle spacers from left to right, but you can't just add one.
Lastly, if you have a steel frame, you can extend the chainstay crimp to make more clearance. It's easier than you might imagine, but needs to be done right.
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