tbh I’d probably just return it at the expense of the seller… it’s not on selling things in this condition
but if you want to fix yourself, then sometimes you can get a purchase using flat blade screwriver or banging in a close fitting torx bit, if that fails you can sometimes melt the end of a bit of plastic (Bic pen with the ink tube removed works well) and shove it into the rounded off screw, let it cool and try turn it loose, failing that then side cutters work pretty well to grab on the head and turn it loose, and then failing that your left with drilling the heads of the screws off completely.