What's the practical way to fix keyword cannibalization?

First confirm it's actually cannibalization. Two pages ranking for the same term isn't automatically a problem; it's a problem when Google keeps swapping which one shows and neither ranks well. In Search Console, filter by the query and look at the Pages tab. If it's two pages flipping, decide which one is stronger, merge the useful bits of the other into it and 301 the weaker URL. If both need to exist, re-angle one so it targets a clearly different intent, and fix your internal links so they point at the right page with the right anchor text.