problem about AJA kona5 output 4K

I am using kona5 and AJA plugins of UE4 to test UHD input & output, I found that UHD singal can input into UE4, but when i config the output, I could not find how to set? the setting UI can see this picture

On kona5 ControlPanel, when I select SDI 4X4K, then HDMI will be set to output UHD automaticly, and I can see the output on monitor. BUT here on the output configuration UI in UE, how to set the output to HDMI? Or how to output 4K with AJA ?

thank you all