Without knowing what have you changed from the default config, it's impossible to tell how to restore it... But it is configured at "/etc/config/dhcp".
If you're double NATing through a DSL modem/router which makes your WAN network 192.168.1.X, you would need to change the OpenWrt router's LAN to something outside that range such as 192.168.2.1. Or otherwise change the DSL router so that it is not using 192.168.1.X, ideally set it to bridge to a public IP.
no its not that, unfortunatly i had to disable dhcp and i was disabling two first checks at dhcp and dns and get it back to not releasing ip becouse than net was gone and now work with adsl dhcp,, that buttons are these
That configuration is called a dumb AP. The main router does all routing and DHCP. The OpenWrt device is a LAN user.
The page you posted are the global server settings. Don't change anything there. Instead go to the bottom of the LAN network interface page. Check the box that turns DHCP (4) off on that interface. Then click the IPv6 tab and disable RA and DHCPv6.