RB751G-2HnD Dynamic IP Port Forwarding

Hey folks.

So I have no clue what I’m doing as I received this router from a friend who helped me out when my other router wouldn’t work with VPNs(unrelated, working fine).
I’ve been trying to forward the UDP ports 8889 and 3478 the whole day by following guides and reading forums etc. and all I can find are guides for static IPs. My IPs are however dynamic and as far as I can tell I either need to make it static somehow or change the rule every time the IP changes?
I’ve gotten as far as IP>Firewall>NAT but I get very confused following the guides when they get to the In.Interface part and the Action part.
I tried setting up 4 rules with dstnat with the Action “accept” on all of them with In.Interface to Gateway and Out.Interface to ether5 (TP is in last slot) but even that didn’t work.
I was hoping you pros could help me out a bit please.
My settings are defualt and untouched, other than password changed and WAN set up. I’m using WinBox 5.26.
Any other info you need just tell me.

Thanks.

when you say dynamic ip you mean that the ip your ISP gives you is dynamic or that the ip your router assigns to your computer is dynamic?
if it’s the latter then make the ip static from ip->dhcp server->leases