In Catalyst, we see a single Salesforce Production Org and its associated Sandboxes as a single Salesforce implementation. If you have purchased the Salesforce connection license for your PRO space, you can connect and sync orgs from a single implementation (1 production and up to 5 sandboxes).
If you want to connect multiple Production Orgs or Sandboxes from different implementations, you need to purchase additional Salesforce connection licenses. Each license costs $1000 per year per implementation.
If you have just one Salesforce connection license on your PRO space, then you can connect just one implementation. It will get created for you automatically. If you have more Salesforce connection licenses, then you need to manually create each new implementation in Space Management, in the Connections page.
Once the new implementation has been created you can then use it in manual setup to connect a new Production org and its sandboxes to your space.