To use an existing survey as a template navigate to Surveys > View.
From here select the "Edit" as highlighted below.
You'll then be asked to give your new survey a title.
Click "Next" when you've decided on a title.
You'll then be taken to the survey question bank as you can see the following view:
Frankli will automatically select the questions from the previous survey you are using as a template. If you'd like to delete or add new questions you can do so in the same way as when creating a survey normally.
The rest is easy! Read more about creating surveys here.