Welcome to the forum.
You need to flash your receiver, with an image, using a USB stick, formatted to FAT 32, on your PC.
Then you download a suitable image, for your receiver, like Black Hole 3.1.0
BlackHole 3.1.0 Multistream Vu+ Uno4K SE | VuPlus Community (vuplus-community.net)
You unzip this image, and copy the vuplus folder onto your FAT 32 formatted USB stick.
You then switch off your receiver, at the rear, plug the USB stick, into the receiver, and power it back on.
You should now get the message requesting that you press the power button, on the front left, of your receiver, and it should start flashing.
Then follow the setup instructions.
Please post back, if you require any further help, need more details, or to update us, with your progress.