What he meant is disable the google form to have multiple responses. I guess that's on the setting of the google form, you just have to click the "icon setting" on the top-right corner of the form and it is under the "General" tab then click again "Limit to one response". So far if I open the form again I can still answer it but if you follow the guide I give that wouldn't be the case anymore and that prevents trolls to troll the form (I have a hunch there will be). Hope that will clarify everything.