Many pen displays need to connect via HDMI to your computer.
You may be in a situation where you don't have any HDMI ports or don't have enough.
There are a couple of options you can look into:
Use HDMI adapters to convert existing ports to HDMI. More here: Using HDMI adapters with pen displays.
Remember that HDMI splitters may not help. More here: Using HDMI splitters with pen displays
If your tablet supports getting a display signal via a USB-C cable, you MIGHT be able to use that as an alternative. See: USB-C DisplayPort alt mode