How can I unlock a PDF and edit form fields once a Fill & Sign signature has been added and the document saved?

I've created a fillable PDF form on Adobe Acrobat Pro 2017.  Form users need to add their signature (captured on-screen using a laptop & stylus) using the Fill & Sign function.  However, once they add it and save the PDF the form fields are locked and cannot be edited.  This is problematic if the user has forgotten to complete a field.  They will need to start with a blank form again (very time consuming).  I cannot find a way to remove the signature nor unlock the form.  Saving the PDF as a copy does not work either.  Ideas?

I'm open to exploring alternate ways to insert on-screen signatures into the PDF.  We have new Lenovo laptops with a stylus that enable us to sign directly on the screen.  I can't use a scribble signature on a PDF form, only HTML, so have been limited to the Fill & Sign Tool.  I don't like using the Comment tool as these can be deleted and are hardy for an inexperienced user to apply.

Many thanks!