I believe iptables --flush should clear out any entries you've made. You can also reboot and clear them (unless you've got scripts bound to your interface up/down config that adds rules).
Basically just need to get any custom iptables rules you made out of there and then re-implement any FW rules with ufw
You can still use iptables alongside UFW, but I only use those for more complex things like port forwarding, masquerading, etc.