How to flash OpenWrt on a Butterfly VPN router?

So I got this router a while ago, and I noticed that it actually uses OpenWrt version:

OpenWrt BTFLY-A 1.3.0 / LuCI 15.05 Branch (0.12+git-16.018.33482-3201903)

However, it's missing a bunch of features that OpenWrt has. I would like to flash an actual updated OpenWrt version to it, but I honestly have nowhere to start. I've never really done this type of stuff before. I just want to be able to port forward with this router.

I tried finding the correct version of OpenWrt, but the info on the router is fairly scarce.

I know that the WiFi device is "mt7620", but that's really all I can find on it.