If you are looking to only clear a single field we would suggest using Form Logic for this. You can add a button to your form, set the Button Action to none, then launch the Form Logic window (Rightmost icon in the top toolbar of the Form Designer). Add a new rule for OnClick of that new button's Control ID, set the Action to SetValue, then set the Action Control ID to the field control you want to clear and you should be good to go. If you wanted to clear multiple fields, simply add all the control IDs to the Action Control ID separated by commas with no spaces.
More info on using Form logic can be found below: