Change Data Value is great, but how do you remove the value completely? Good question!
1. In the flow step, choose the field you would like to clear and type in NULL (all caps) as the New Value.
2. Boom! I bet you didn't know that! After the flow step finishes, the value of the field you chose is cleared.
Leaving the new value blank or simply entering a SPACE will not truly empty the field. You have to type in NULL. Also, remember, flow steps can't be undone after running.