You can do this in principle. However, the Fritzbox will then act as a second router and not as a repeater. This means you have a second subnet or a second WLAN name. The devices, e.g. mobile and SmartTV, will not be able to see each other if one device is connected to the Swisscom router and the other to the Fritzbox.
I think you are looking for a classic repeater or a powerline device.

I think so-you have to switch the 4060 as a repeater

Hi HuiBuh - I did exactly what you want to do. Via a long cable from the Sunrise Box to the Fritz!4060, which you can configure as an IP client. Then you don't have a 2nd subnet as described by kupferwerk.
By the way: Fritz has lots of good tips and instructions - and I can only recommend their support. If you receive an answer to the ticket (approx. 2 days), then the response times are very short (a few hours).
And another thing: the 4060 has really good power, the reception is now tiptop everywhere.
Have fun and good luck!