Unfortunately, you cannot reset a campaign. We cannot remove the donations that a campaign has already accumulated and reset it to 0. What you can do though is use the same information like the theme, images, videos, campaign name, etc. You would just have to redo it and copy-paste last year's content.
For the new campaign to have a unique URL and to avoid confusions, you may try adding up a year at the end of the campaign like "Fundly Run 2020".