Disconnect monitor cable from the 210, connect to mobo graphics port, boot to bios, check set to use igpu, boot to OS, download/install driver from AMD.
Guess you better reconnect to the 210, read the mobo manual for instructions.
Some more INFORMATION REQUIRED WHEN POSTING A QUESTION may help someone offer further suggestion if you still have troubles.
Your other thread I tried to connect my monitor cable to the onboard graphics
Hiya welcome to the forum.
Without posting the system specific details required it will be very hard to answer your question
Without knowing exact model of motherboard I will have to speculate. Usually Multi monitor options in BIOS are for using both integrated and discrete GPU at same time, but your saying your not getting your discrete card to work. What your going to want to look for in your UEFI / BIOS is
Integrated Graphics Devices Configuration setting/s . Check to make sure it is SET to PEG for discrete cards and plugin your HDMI to the Vega11 after powering down and rebooting
IGD = Integrated
PEG= your vega11
This is all speculation of course all manufactures use different but same based settings. PLEASE LIST YOUR FULL SYSTEM SPECs so others might try to help you.