Hi can anyone help me with the size of screw I would need to replace

katrinarobinson82 that is perfect. I would take the headset to my local hardware store. Mom and Pop hardware is still the best since the larger warehouse style hardware stores do not quite have the personal touch. Show them what you are looking for. Those will most likely by small metric threads. You can try the screws right there and get the size you need. The other places I would try are Jewellers, watchmakers and local RC and electronic clubs. Those people never throw anything out and you'll be surprised what you'll find.

Since those look like inserts, you can measure the hole with a pair of calipers to determine which size you will need. Local machine shops and technical colleges can help you with that as well.

This headset is not a valve index headset id suggest reposting it in the Vive headset section you may have better luck there. I suspect this headset is the HTC Vive Pro, but I am not sure you would know better than me