That’s really odd. I guess you dragged it off screen? The only way I can think of is to manually edit and delete the tilt meter from the HUD xml file.
You can locate your HUD file here: C:\Users\(your system username)\AppData\Roaming\DriveHUD\LayoutsV2
Open the file in notepad or an editor, and then look for this line, delete it and save:
<HudLayoutTool xsi:type=”HudLayoutTiltMeterTool”>