To update an SObject field from an OmniScript, the standard and recommended approach involves two key server-side components. A DataRaptor (specifically a DataRaptor Post Action, formerly Load) is the dedicated tool for performing Data Manipulation Language (DML) operations like creating or updating Salesforce records.

An Integration Procedure is used to bundle this and other server-side actions into a single, reusable transaction. The OmniScript calls the Integration Procedure, which in turn calls the DataRaptor to perform the update. This pattern is a best practice as it minimizes client-to-server calls (improving performance) and separates business logic from the user interface.

B. SOQL Query: A SOQL Query is used exclusively for retrieving (reading) data from Salesforce objects, not for modifying or updating records.

C. API Actions: API Actions are primarily designed to call external REST APIs. While you could call the Salesforce API, DataRaptors are the native, more efficient tool for SObject manipulation.

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1. Salesforce Help, OmniStudio Documentation, "DataRaptor Load": "Use a DataRaptor Load to create, update, or delete Salesforce data... A DataRaptor Load receives data in JSON or XML format, and writes the data to Salesforce objects." This source confirms that DataRaptors are the correct tool for updating SObjects.

2. Salesforce Help, OmniStudio Documentation, "Integration Procedure Actions": The documentation lists "DataRaptor Post Action" as a primary available action within an Integration Procedure. It states this action "Runs a DataRaptor Load or a DataRaptor Turbo Action." This confirms that Integration Procedures are designed to orchestrate DataRaptors for data updates.

3. Salesforce Trailhead, OmniStudio Architecture, "OmniStudio Service Management": "Integration Procedures run on the server and are the recommended way to save data from an OmniScript... An Integration Procedure can call a DataRaptor to load the data into Salesforce." This reference explicitly states the best practice of using an Integration Procedure to call a DataRaptor for saving data.