How can I find an open port I can host Blockland on?

[Mister Cheese]

So, we've gotten a new router at our house, and unlike my previous, port 28000 is not open, and my dad is not letting me open ports. How would I be able to find an open one, like using a program for it?

[Ad Bot]

[Mister Cheese]

Nevermind. tried port directly below 28000 and it worked. Locking.