XPS 15 9550 Heatsink standoffs pooped out from motherboard

It's unlikely the warranty will cover this -- but very likely the parts are not available separately from the system board.  You can try contacting Dell but this will almost certainly be expensive - and treated as an out of warranty repair.

Thanks for reply. Here is pic

The thing you're going to need to explain to support is why that happened -- in other words, what were you doing when that occurred?

I did nothing. Few months ago I noticed one standoff pooped out and few days ago I opened laptop to clean dust and there was second one with same problem.

About all you can do is contact Dell support and see what they say about a warranty repair.