If you are using Maya, this video is a quick guide on how to bake ambient occlusion to textures to then allow it to be exported as glTF from Unity.
A few things to note:
Needs to be baked to 2nd UV
Unity will not show the AO (Ambient Occlusion) correctly, but it will come into Plattar fine
Export the FBX file out of Maya and then into Unity (OBJ will not work)
Only use these (below) fields when exporting to Plattar