Build your Uno R3 no longer detected

I have an official build your own uno R3 with USB-C and an ATMEGA16U2, but now it is not being detected when I plug it in to both my Mac and my pc. This board doesn’t have the reset jumpers next to the usb chip, it does have jumpers at the other side and I tried resetting using that but no joy. How do I set this board to be reprogrammed with dfu programmer or flip?