If you need to pass data into specific fields of the Workflow Task form, follow these steps:
Step 1. Put the Web Form XML schema prior to the Workflow task activity. This activity should get an input data stream that is in the format of the Form's XML schema. Use a Data Mapping Activity to map the source data into the this target XML schema as a prior step in the flow.
Step 2. The next activity should be the Workflow task and make the Consume stream option of this activity to True.