You need to access to your local server from outside of local network using SSH from the command line.
Solution:
You need to map a port in your firewall to allow the firewall pass the remote access connectin from ou public IP access to your local server, for that search port forwarding configuration and map there you raspberry local IP, now you can create an external connection to your raspberry if you user your public IP and the selected port.
Use the following steps to jump between any raspberry system:
1.- simple remote access connection using the same user.
sudo ssh hostname/ipaddress
2.- change the user
sudo ssh user@hostname
3.- close the session
sudo exit