Update iptables - set ttl

It my firs post on this forum. I want to share internet, using wifi from first smartphone to second smartphone. My operator taboo to share wifi. Second smartphone - oucitel c21. It cannot root. I decided to use router-repeater - dlink dir 300 b1. I installed Openwrt https://openwrt.org/ru/toh/d-link/dir-300revb. But I need to change ttl on router. I was founded in internet, what necessary add in file /etc/firewall.user: iptables -t mangle -A POSTROUTING -j TTL --ttl-set 65. But initially in Openwrt installed iptables ver. 1.4.21. This version don't support command --ttl-set. How I can update iptables on router? Мaybe there is another way to solve this problem?