Understand record update action
The update record action in data access of workflow is similar to the the action of the same name in deluge script. In the latter, you need to create the code form the action. Instead, you can use the predefined action that is available under data access.
When you create a workflow for a form with Update Record action, it implies that updating a record using that form should subsequently automate updates in the field values of other records. You can run this action with or without a criteria. This action allows a second level for defining criteria. This criteria determines which are the records that need to be updated in the selected for, while the former determines what conditions need to be satisfied for the action to be called when the form is updated.
You can select the fields (apart from the mandatory fields) that need to be updated and specify the field value.
Let's assume you have a Product Inventory Management application. You have a Product Details form and a Stock Management form. The defined criteria states when the Number of Units left field equals 2 run the update record action. The action is based on the Stock Management form. You have selected the Stock Status field and specified field value as Out of stock. When a record is updated using the Product Details form, if the criteria is satisfied, the Update Record action is called and the Stock Status in that record will be updated to Out of Stock.