Installation folder - sceneries check your FSX\addon scenery folder. You must have these 3 folders Vietnam War Project Vietnam War Project Under Fire Vietnam War project Fictive LZ and in these folders : scenery and texture i.e. My scenery folder content

If OK, we can activate the 3 sceneries folders. I'm sorry, this is french version of FSX. Upon starting FSX, go to Settings > Addon Scenery, and browse to the location of the folder "Vietnam war project". Click on it and press OK (don't open the folder) to enable the scenery - it should then appear at the top of your Addon Scenery list.

Repeat for the 2 others folders.

Close FSX and restart. The Under Fire scenery must be at the top, above the 2 others.