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The Assign Contacts to Projects page lets you assign multiple contacts to multiple projects at once.
Watch the walkthrough
Explanation video: https://www.loom.com/share/33438b69d6bd46a2995c6312d5cdb024
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Go to the Contacts page
Select the More Options button
Select Assign contacts to projects
You arrive on the Bulk Assign page
There is a column for each project and a row for each contact.
Use the tick boxes dropdown list to add/remove contacts to/from projects (to add a contact to a project, select Enrolled from the dropdown list)
Press Save
The assignments are done and you arrive back on the Contacts page