Editing a drop down menu in a form can be done through the Form Builder on the Web Portal.
In the Web Portal, go to Forms > Existing Templates > Select the edit arrow for the Form you would like to edit > Form Builder > Find Section with the drop down menu you want to edit > click on the title/question of the dropdown in the form. On the right hand side in field settings you will see the Items box, your list of dropdown answers will be available.
Answers can be deleted by selecting delete when hovering over them, re-ordered by dragging the answers into the order you want, sorted alphabetically, and edited (double click on word to be changed).
New items can be added through the items box > Add.
Once you've sorted the dropdown answers the way you want, then Save Draft > Deploy / Publish Template.
Please note: To ensure the edited form is up to date on the App, allow the app to sync on the device fully before going into the form.