On your existing OH server use this command sudo openhab-cli backup --full.
This will make a zipped backup and tell you the location e.g. /var/lib/openhab2/backups/
Next use something like filezilla to transfer the backup from the server to your PC or move it to a USB stick.
Now on your new OH server make a backup, same steps as above, to create a backup file. Once the file has been created you can delete that backup and move the backup from existing server to the backup location.
Once the file is in place, stop OH with sudo systemctl stop openhab2 then use sudo openhab-cli restore /var/lib/openhab2/backups/ and restart OH with sudo systemctl start openhab2