Note: Since February'22 release below actions are done automatically on the first sign up.
In Salesforce, Person Accounts are found simultaneously in both Account and Contact objects. Analyzing and merging these dupes in Accounts (Person Account) will also resolve the duplicates found in Contacts.
Note: Salesforce does not allow merging Contacts of type Person Accounts. To exclude such Contact objects from analysis we recommend applying the following filters to your datasets (using Advanced SOQL switch)
For "Contact" object dataset,
Account.isPersonAccount = FALSE
For "Account" object dataset, we recommend the following filter
isPersonAccount = TRUE
Learn more from Salesforce
Considerations for Using Person Accounts (salesforce.com)
Guidelines for Merging Duplicate Accounts (salesforce.com