ufw is an easy to use firewall.

View rules with ufw status numbered

You can allow TCP traffic from 10.0.0.1 to port 22 with:
ufw allow proto tcp from 10.0.0.1 to any port 22

In case you've broken some system and need to add/remove some rules, you can edit the rules under /etc/ufw/: user.rules and user6.rules for IPv4 and IPv6 respectively.

As an example, suppose the wireguard network is 10.0.0.0/24. You can configure ufw to allow SSH access as follows:

• allow wireguard tunnel port: ufw allow 51872/udp
• allow ssh access only from wireguard network: ufw allow proto tcp from 10.0.0.0/24 to any port 22
• enable ufw: ufw enable