Migrating all settings from hap ac2 to ac3

Hello,
I expect this to be answered somewhere, but I did not find it with a search, so I’m asking and sorry if it’s a duplicate.
I have a HAP ac2 router at home with a lot of custom settings. I also have a new HAP ac3 router. i want to switch to the new router and make it as painless as possible.
What is the easiest way to migrate all of the settings - firewalls, vpns, tunnels, services, etc ?