@feffer777, why didn't you just ask me in the original thread?
You browse to Services > Dynamic DNS
If you don't see it, additionally install: https://openwrt.org/packages/pkgdata/luci-app-ddns
The OP can additionally install: https://openwrt.org/packages/pkgdata/ddns-scripts
Also, all DDNS scripts available: https://openwrt.org/packages/table/start?dataflt[Description_wiki*~]=Dynamic+DNS+Client+scripts