Converting from WGS84 to NAVD88

[JamesStewart-Moore1]

I have a DJI drone that captures all data (horizontal and vertical) in WGS84 (meters). I want to be able to process the drone data so that the result is in NAVD88. I am doing the data processing in Drone2Map and the only options for vertical datums in the the "output coordinate system" are the EGM datums. Is there an easy way to convert the WGS84 vertical coordinates into NAVD88 coordinates?

I found NOAA's VDATUM online tool, but I only somewhat understand what I can do with the transformation data it provides (e.g. multiply the WGS84 or EGM96 data by the correct scale factor).

[CodyBenkelman]

The output coordinate system is not controlled by the coordinate system of the input images.  It defaults to UTM but you can use control points with vertical datum of NAVD88 to define your output coordinates:

Vertical reference—Drone2Map for ArcGIS Help | ArcGIS 

If you have GCPs, the height of Drone2Map products use the vertical units and vertical reference model used by the ground control. If you don't have GCPs, the output products are created using the vertical units and vertical reference model of the images.