You may have a set list of tasks that need to be repeated on a regular basis. If you don't have a set schedule for these tasks, you can reset all of your "finished" tasks so that they are "unfinished" all at once. Follow the steps in the image below:
Note: This only works for the "Finished progress status of your tasks. If you have any other tags, progress statuses other than "finished," etc. those will not be reset and will stay the same.
If you need your Tasks to reset automatically on a daily, weekly, monthly, or yearly schedule (rather than manually resetting them all at once) you should create repeating Tasks instead.