Have him install 1 RAM stick in Slot A2 (2nd from the CPU) and then Clear the CMOS like this:
Unplug the PC (PSU).
Then press the Power Button for at least 30 seconds.
Use a flat headed screwdriver to short the CLR CMOS (CLRTC) Jumper (Touch both jumper pins with the screwdriver) for at least 15 seconds.
CLRTC jumper location can be seen on page 1-2 here:
E15236_TUF_GAMING_X570-PLUS_WI-FI_UM_WEB_060319.pdf (asus.com)
Plug the PC back in.
Press the Power Button to turn the PC on.
Repeatedly tap the DEL key
A screen should come up telling you to press the F1 key, do that.
Set the Optimized Default settings and Press OK (this is on the EXIT tab)
Save and exit the BIOS.
Tap the DEL key again to enter the BIOS and change any settings you want changed then save and exit again.
He may have to do this 3 or 4 or more times before it works.
If that works have him shutdown the PC and in stall the other RAM stick in slot B2 (4th from the CPU) and then restart the PC.