That's not good. Guess the only way to get access again if this happens is a reinstallation.
Would be better the app would switch to reachable nodes after a long enough time without connection.
Discussion
it looks like if you mess up the config you can force the node with:
/path/Haveno --xmrNode=192.168.1.1
but the user said it won't actually take a comma separated list of IPs like the "custom nodes" field says it will
¯\_(ツ)_/¯