How to pairup-bind static local IP to MAC adress?

Hi,have a few devices on mine local network,how bind mac adresses of these devices to local static ip"s?for example xx:xx:xx:xx:xx-,how do that from web interface?Device is with OpenWrt 18.06.2 r7676-cddd7b4c77 / LuCI openwrt-18.06 branch (git-19.020.41695-6f6641d) i know,i know that not fresh version,but using what is possible with TP-Link TL-WR740N/ND v4

Not sure how you do it in LUCI as I haven't used the GUI in a long time... but from command line just login and edit /etc/config/dhcp to add a block like this:

config host
        option ip ''
       option mac 'xx:xx:xx:xx:xx:xx'
       option name 'SomethingMemorableForYou'

Update: In LUCI go to "Network -> DHCP and DNS" then scroll way to the bottom and find the section that says "Static leases". Hit add, fill in your info, and apply.