Based on the available Salesforce actions in Clay, you cannot directly convert a lead to a contact through the Clay integration. The supported Salesforce actions are: β’ Create Recordβ’ Lookup Recordβ’ Update Recordβ’ Upsert Objectβ’ Lookup Records via SOQLYou'll need to perform the lead conversion directly in Salesforce.
Sources:Salesforce integration overview | Documentation | Clay UniversitySalesforce x Clay integration | Clay.com