Pressure Rivet Nut Tool Kit, 750PCS Metric Rivet Nut Combination (M6/M5/M4/M3), Suitable for Furniture, Decoration, Automotive, Marine and Industrial Applications

Yeah, this is basically exactly what happened to my mom's car. I think I used an M10 rivet insert but I would just get a kit like this one (https://a.co/d/07P7Zl46) that has a variety of sizes and just choose the closest one. I filed the raised part a bit flatter to make sure it would seat somewhat flat and then bought some bolts from a hardware store