Rebuild landscape collision?

Hey just migrated my project to the new engine. Most things work as they should.

Re-sculpted some of the landscapes in my levels, after a pass with the retop tool ragdoll collisions cause severe lag upon colliding with the landscape. (like dropping from 80 fps to 5 fps)

I suspect I need to rebuild something but nothing under the ‘build’ tab seems to do the trick, in standalone I get a message ‘LANDSCAPE PHYSICAL MATERIAL NEEDS TO BE REBUILT’

I think I’m just missing the button but I can’t find it for the life of me.