The problem is, that you are using "4_Levels" for the Face, which is static Normal maps based (not texture). And those Normal maps cover the face only.
So no matter what mask you are applying, levels are not going to span outside the face.

If you insist using Levels effects for the rest of the head (but not for the face - as I understood based on your screenshots), then in addition to making a custom mask, you have to tweak Normal map.
First Embed it and then Launch Normal map to open it in image editor. And then use clone brush (or by some other means), for replicate normal effect to the rest of the head - based on UV.

So here is a quick example, where I used a clone brush in Photoshop to tweak Normal map within the Micro effect and made a quick mask to apply to the area above forehead only.

75% of original size (was 668x19) - Click to enlarge

Here is an IC7 manual part concerning facial wrinkles. You have to buy SkinGen Premium Plugin.
SkinGen Premium Plug-in for Character Creator Online Manual - Using Normal Templates (reallusion.com)

I want to put all skingen (tertiary) to all forehead. I made custom mask to cover all forehead but it still doesn’t cover . How can I put skingen texture to all forehead?