You could export your collected forms data to a csv file (which you can open in Excel or another spreadsheet application) and then edit the data as needed using cell formulae.
To access your historical forms data, go to your Weebly site landing page and, in the left-hand sidebar, click on the "Website" parent item, and then click on the "Overview" child item. Below the header zone, click the "Form Entries" button. This will take you to the page that lists all of your form submission data from the time you launched the form. In the upper-right corner of the page, click the "Export All" button to save the data as a csv file. Now open that file in a spreadsheet application (form fields will be parsed into separate columns). You can use cell formulae (in a blank column that references a data column) to make bulk modifications to the submitted data.
