When a record in Channeltivity is synced with HubSpot, a link is created between the record in Channeltivity and the one in HubSpot. For example, when a Partner submits a new Deal Registration or Referral, Channeltivity creates a Deal in HubSpot with the same information and keeps those records linked. The concept of linking is used by all of Channeltivity's integration points with HubSpot.
How do I unlink a Deal or Referral?
To unlink a Deal Registration or Referral that is linked to Deal in HubSpot, click the HubSpot button on the record's details page in Channeltivity > Unlink. 
Deal Details Page - HubSpot Menu
Confirm you want to unlink the records by selecting the "I'm sure I want to unlink the Deal" checkbox > Unlink.
Unlink a Deal Window
How do I link a Deal or Referral to an existing Deal in HubSpot?
A Deal Registration or Referral that is not linked to a HubSpot Deal can be linked to an existing Deal in HubSpot. If a Deal Registration or Referral is already linked to a Deal in HubSpot, you can unlink the records using the instructions in the above section.
To link a Deal Registration or Referral to an existing Deal in HubSpot, click the HubSpot button on the record's details page in Channeltivity > Link to an existing Deal in HubSpot.
Deal Details Page - HubSpot Menu
Paste the URL of the HubSpot Deal that you want to link the record to. Then, select which system (HubSpot or Channeltivity) should be the master for the sync for mapped fields with conflicting values and click "Next."
Link Deal Window
Confirm you want to link the record to an existing Deal in HubSpot by clicking the "This is correct. I wish to link these records" checkbox > Link.
Confirm HubSpot Deal Link Window
Related Documentation:
What is the Deal Registration Module and how does it work?
HubSpot Integration: Deal Registration - Overview
What Is the Referral Module and How Does It Work?
HubSpot Integration: Referral - Overview