Create a wireguard interface on each end, add the keys to them, open up the allow list for each subnet, assign a IP from a /30 (or /31) subnet on each end, set

Create a wireguard interface on each end, add the keys to them, open up the allow list for each subnet, assign a IP from a /30 (or /31) subnet on each end, set static routes to point to other end or use a dynamic routing protocol. There are tools to automate this like wg-quick and systemd-networkd, depending on your preference.