Options Other Than Absolute Height Elevation Unavailable

[Yex4]

I have created a custom elevation surface and am trying to set some lidar data's elevation properties to use it, however I have no option to.

I'm not really sure where to go from here as working with elevations and lidar is very new to me.

[tomESRI]

Are you working in 2D or 3D?

[Yex4]

I'm working in 3D

[tomESRI]

There should be a ground surface layer for the lidar layer in your contents. This can be used to manipulate elevations rather than the lidar itself. In the ground layers, "customise" ribbon, you can merge the two. 

https://pro.arcgis.com/en/pro-app/latest/help/mapping/layer-properties/elevation-surfaces.htm#:~:tex....

[Yex4]

I've already done that part, I'm now trying to get the lidar layer to measure the elevation of points using the new ground surface I've made so I can get relative elevations and not use sea level.