Setting a default gateway for a container

(If this is the wrong place to post this let me know)

I’ve got 2 networks on my Debian server:
DSL: def.gateway 192.168.1.1
4G: def.gateway 192.168.2.1

Currently all of my containers go through the DSL by default, as it’s the main network card on my server. I want to set plexmediaserver (running in host network mode) to use the 4G network as it’s default gateway, so all remote streaming will be transferred through the 4G network (better upload speeds).

How would I approach this?