You need for installation variant C:

Narrow helmet adapter

Tilsberk head-up display

Tilsberk head-up display App

Adhesive pad for narrow helmet adapter
For which helmets is installation variant C suitable?
Installation variant C is often used for helmets with sun visors whose fabric in the area of the mounting surface (marked red) is fixed / non-stretchable.

Note
Before installation
For secure mounting, all adhesive surfaces must be clean, dry, and free of dust and grease. Therefore, please clean all smooth surfaces thoroughly with an alcohol-based cleaner such as spirit or rubbing alcohol before mounting. Adhesion is better on surfaces made of fabric - nevertheless, these surfaces should also be cleaned.