Welcome to the Community, Shausheabouwh55!
You are completely right. Sunrise only pays for the very first basic installation from the building basement up to one single main OTO box inside your apartment. To my knowledge, any further internal adjustments, moving the OTO box to another room, or pulling ethernet cables through the walls are then already private modifications.
Sunrise does not offer in-house electricians for these custom adjustments. This might only be possible for a fee, but I am not entirely sure about that. I do think you should hire a private electrician or an authorized network technician for something like this.
If you just need a stable connection in your room, pulling a standard Cat6a or Cat7 ethernet cable from the living room router through the existing wall pipes to your room is already the best and most robust solution.
Alternatively, a Sunrise repeater would also work, which however causes monthly costs. Or you can buy a third-party device yourself. It will be compatible, but it won’t be directly integrated into the Smart WiFi mesh system of the Connect Box 3. Powerline adapters would also be an alternative, although I am no fan of them at all since they are often sources of interference and do not always work.
Cheerio cosmo