It’s difficult to get in there underneath the factory deflector. You could cut the sides of the deflector and then bend it up to do all your work. Make sure you deburr everything inside and don’t go so deep into the baffle that you can no longer reach it with any of your tooling. And then braze or weld the deflector back down. Or screw your new deflector back in its place. Make sure your hole is completely covered by the deflector or it will burn your brake handle