Like Cali said, I'm going to assume you're talking about the plastic since euro bracing a bow is almost impossible and none come from the factory with it. Pics would help a lot.
you can order new plastic from the manufacturer and replace it you have to remove all the silcone and clean it good before install new one ,you have to remove some of the water 1/3 to 1/2
I replaced the center brace for my Perfecto 75 gallon tank (not RR).
What a PITA!!!! If I had it to do over I would have just purchased a new tank. The cost of the brace & silicone, the hours scraping etc. was not worth it.
I would not try to replace the brace w/water in the tank.
Think this out fully before starting this project.