Try pressing F and the camera should focus on the ground plane. You might be able to see it then.
If you still dont, make sure it is selected (either in the viewport or if you cant be sure, then in the scene manager on the right) and then move it around using the transform palette. You can see how to find the transform palette here:
AC26 ARM // MBP M2 Max // Twinmotion | Corona | Rhino