Yeah @kurulumu-Net you can change port in config.json in one of the NodeBBs and change to the same port in the proxy-pass part of the corresponding nginx config.
Default port is 4567, one will need to be changed.
I would like to request you to add documentation of NodeBB hosting on Linode.
But I can tell you that the Ubuntu upgrade on Linode doesn't work well - they say so too - and I'm thinking of migrating to Debian (if that helps).
the Ubuntu upgrade on Linode doesn't work well
I can't imagine it would... OS upgrades usually are a little suspect, it's usually easier to just start fresh and migrate NodeBB back onto it, although I definitely get why an OS upgrade would be preferable in some setups.