When I had to help my dad with his ESA form a few years ago (he was unable to complete them himself) there was a section to complete if you'd had help completing the form.
I now find myself helping him with his PIP2 form - my dad wouldn't have a clue due to his ill concentration caused by his Ankylosing Spondylitis - but there is no section to complete if you've had assistance, nowhere to advise whether you were able to complete the form yourself.
Should this just be added to the extra information section at the back?