How to identify a User from 3-rd party in salesforce?

Use Third-Party Data to Update and Add Records to Salesforce
A rule set up by your Salesforce admin compares your accounts, contacts, and leads to data from a third-party source—Lightning Data or Data.com. Depending on how your admin sets up the rule, your records are updated as information changes. Or your admin can give you purchase credits to import Lightning Data records to add to Salesforce as accounts.

REQUIRED EDITIONS AND USER PERMISSIONS
Available in: Professional, Enterprise, Performance, and Unlimited Editions

USER PERMISSIONS NEEDED
To update records:
Edit on accounts, contacts, leads, and Read on the custom and external objects included in a data package
Check for New Data Matched to a Record
Look at the data status to see whether a data service has new data matched to an account, contact, or lead.
Discover Companies to Import as Accounts in Lightning Experience
Fill your pipeline with ideal prospects. When your Salesforce admin sets up a Lightning Data package, you can find companies to target and import them into Salesforce as business account