You can edit and modify an existing workflow in HappyFox Workflows. Here are the steps to be followed:

1. Log in to HappyFox Workflows.
2. Open the required workflow to be modified. 
3. Disable the workflow using the toggle option. 
4. Modify the workflow as needed. You can edit existing actions or add new actions. 
5. ‘Save and Test’ all the actions. 
6. Verify the actions performed in the sample event and then enable the workflow.