Case has 2 usb 3.0 and mobo has only 1

[trollface61]

The asrock ab350m pro4 has just 1 USB 3.0 header but says that 2 usb 3.0 are supported so I don't understand

 

[feelinfroggy777]

1 usb 3.0 header supports 2 usb 3.0 connections. You just need to plug the blue cord into the usb header and both case connections will work.

 

[JackNaylorPE]

The header usually provides for support of two (2) USB connections on the case front.