Foliage doesn't stick to environment anymore/ reapply?

Hi I’m new to Unreal and trying to get into the landscape tools.

When opening my terrain again, after I re-sculpted it, the foliage didn’t stick to it anymore. Is there a way to stick it again? Someone wrote to reapply, but I can’t find that function.
Also I can’t erase the floating foliage with the brush.

When I create new foliage on the same map, it sticks to the terrain when I scuplt.

Generally, I find the documentation a bit thin. Can you guys recommend some in-depth documentation or tutorials for landscape in general and landscape lighting?
I don’t want to spam the forum with noob questions :stuck_out_tongue: