The easiest and most robust way to fix a headlamp on a (caving) helmt was by simply drill the necessary holes and fixing the brackets with screws.

You find the description for this in our mounting instructions (that you got with your manual).

Of course that depends very much on the helmet model used. Many modern helmets often use a foam layer and it's more difficult to access the hard shell..

If you are not allowed to drill holes in your PPE there is a good alternative here.