Mass insert Account or Opportunity Contact Roles with Data Loader

Prepare a .csv file with the required columns

• AccountId: The ID of the Account associated to the Contact.
• ContactId: The ID of the Contact(s) to be assigned or updated.
• Role: The Role name to be assigned. To find the Role name:

• In Salesforce Classic: Navigate to Setup and enter Contact Roles on Accounts into the Quick Find box.
• In Lightning Experience: Contact Roles on Accounts is currently unavailable in Lightning Experience. Review Add and Manage Contact Roles in Lightning Experience for more information.

• IsPrimary: Specify whether the Contact being assigned is designated as the primary Contact for the Account. Enter TRUE for the primary Contact and FALSE for all other Contacts. 

• OpportunityId: The ID of the Opportunity associated to the Contact.
• ContactId: The ID of the Contact(s) to be assigned or updated.
• Role: The Role name to be assigned. To find the Role name, navigate to Setup and enter Contact Roles on Opportunities into the Quick Find box.
• IsPrimary: Specify whether the Contact being assigned is designated as the primary Contact for the Account. Enter TRUE for the primary Contact and FALSE for all other Contacts. 

Insert Account Contact Role or Opportunity Contact Role records with Data Loader

1. Log into the Data Loader.
2. Select Insert.
3. Select Show all Salesforce objects.
4. Select Account Contact Role or Opportunity Contact Role.
5. Select Browse and choose your file.
6. Click Next and you will be prompted for the number of records the file you selected contains, click OK.
7. Click Create or Edit a Map and Auto-Match Fields to Columns (If the fields don't auto map, drag and map accordingly).
8. Click OK and then click Next.
9. Click Browse and select the location you want your 'success' and 'error' files to download to.
10. Click Finish and choose Yes when prompted.