Sync your existing contacts
The "Sync to CRM" button on the Contacts screen pushes all existing contacts to every connected tool. Duplicates are skipped automatically.
Integrations automatically send only new contacts. You move the history over manually, once.
How to sync existing contacts
On the Contacts screen there is a Sync to CRM button that pushes all your existing contacts to every connected tool. You can also sync to a single destination from that tool's manage dialog, with a "Sync existing" button.
Already-synced contacts are skipped automatically, so it is always safe to press again, with no duplicates.
What is not included
Pipe connections (Zapier, Make) send only new contacts in real time, so they are not part of the history backfill.
For the general picture, see how integrations work.