Window handle screw replacement

You can get a rivet kit for easy money:

https://www.screwfix.ie/p/magnusson-hand-riveter-10-1-2-265mm-/589pr

You would just need blind rivets of a suitable diameter then to replace the existing ones.

https://www.screwfix.ie/p/easyfix-blind-rivets-3-2mm-x-10mm-500-pack/14233

whatever you do remove the glass before you drill out the old rivets. or you will break the glass

years of experience here. if u drill the rivets with the glass in you will more than likely break the glass.