How to delete your messed-up Flow so you can create a new one that works
If you're here, it's because your Flow settings got messed up and the easiest way to deal with this is to delete it and then redo the steps to create it again, making sure you get the settings right this time.
To delete your existing flow:
Go to Setup and then, on the lefthand menu, way down under PLATFORM TOOLS, find & click Process Automation and under that, click Paused and Failed Flow Interviews.
Click on All Paused Flow Interviews (upper left) to drop down a list of views and select All Failed Flow Interviews instead.
Now you may see a list of rows–one for each time you tried to add a lead & the Flow failed. If so, then for each row, click the down arrow on the far right of that row to get a drop-down then select Delete and repeat that for each row until they're all gone.
When there are no more rows in that list, click on Flows (on the lefthand vertical menu) and find the one you created but do NOT click on the name. (It should be named "Automatically add an email task to every new lead").
On the row for that Flow, on the far right side, click the down-arrow and select View Details and Versions.
Then on the page that comes up, there will be one or more rows with each row representing a different version of the Flow you created. If any row says Deactivate (blue) on the lower left, click it to deactivate that version of the Flow.
Now the Delete button (upper center) should be clickable so just click it to delete the Flow.
Then click OK in the popup to confirm.
Now redo the steps to create the Flow:
Start with Step 35 and continue until you finish Step 71.
Then, if you were trying to get the lead added in Step 117 (with the first 2 letters of your first name + the last 3 letters of your last name) when you ran into the Flow error before, then you can restart now at Step 103 and go from there.
Or if you were adding Miles Dyson using the web form in Step 151, when you ran into the Flow error before, then just try adding him again now using that same webform.
Or if you were running the grader when you ran into the Flow error before, now you can just go ahead and rescore again, using the Developer Console, and refresh the page.