DIND rootless - how to change default gateway

Hi there,
How can I change the default root as ip route change default via dev net1 is not permitted?

The DIND-rootless has a second interface, exclusively connected to this container. I want all traffic flowing through this interface, so I have to change the default gateway, how can I achieve this?
Moreover, how can I proof this as traceroute is not permitted as well?

thank you