Plugged home assistent router into new router. How to access ha?

I got new internet and the they tell me the router it came with doesn't do 2.4.

So I just plugged my old router into the new one and figured it's maybe a good idea to have a separate HA network and do all my internet stuff on the new one.

Everything works. Only issue is that I need to switch my phone to the old wifi to access HA.

Is there a good way around that? How can I make it so my HA instance running in Proxmox on my old router can be accessed when my phone is connected to my new router.

Or, correct me if I'm doing this all wrong!