After you unzip/extract the files you copy/paste both folders in to x-plane 12 / custom scenery. The Airport and the mesh.
Load xp and when you get the options to select aircrafts quit xp. Open up custom scenery folder find there scenery_packs.ini open with notepad and
cut SCENERY_PACK Custom Scenery/z_BIKF_mesh_xp12 (Xometry)/ from the top, and paste it at the bottom or under ortho4xp if you have any on the list like so.
And save the file and exit.
Example from my scenery_pack.
SCENERY_PACK Custom Scenery/zOrtho4XP_+70-009/
SCENERY_PACK Custom Scenery/zOrtho4XP_+70-010/
SCENERY_PACK Custom Scenery/zOrtho4XP_+71-008/
SCENERY_PACK Custom Scenery/zOrtho4XP_+71-009/
SCENERY_PACK Custom Scenery/z_BIKF_mesh_xp12 (Xometry)/
SCENERY_PACK Custom Scenery/z_ENGM_Scenery_Mesh/
SCENERY_PACK Custom Scenery/aaa_Boundless_Library_v1.4/
SCENERY_PACK Custom Scenery/SAM_Library/
SCENERY_PACK Custom Scenery/SAM_WorldJetways/
SCENERY_PACK Custom Scenery/simHeaven_X-World_Vegetation_Library/