To create a network bridge with netplan you have to create a file
network: version: 2 ethernets: enp6s0: dhcp4: true bridges: br0: interfaces: [enp6s0] dhcp4: true optional: false macaddress: <some mac>
Make sure to place a mac address in and replace the interface name enp6s0 with yours.
Then run sudo netplan apply.
The machine gets a new IP from dhcp so make sure you have it configured in your dhcp before or have a local console ;-)