Edit Questionnaire Templates
First, navigate to the Knowledge Base ('Setup' >> 'Knowledge Base') and click on 'Questionnaire Template' under the 'Questionnaires Templates' section:
Next, click on the questionnaire you'd like to edit. Select 'Add/Remove Section' and then 'Subsections' to add/remove edit fields within that specific subsection:
Note: You can't edit a 'Zoom' questionnaire in this setting. If you want to edit one of those template questionnaires, you'll need to select 'Copy To' and add that questionnaire to your templates (which will happen automatically once you click 'Save' within the 'Copy to' pop-up). Then it will be editable.
After you've edited/added/removed any subsections make sure to save the questionnaire.