Without linking your Google Form to a new spreadsheet
1. Duplicate the tab collecting Form Responses
2. Rename this duplicated tab as Archive, if desired.
3. Select and delete these rows from the tab collecting Form Responses
All new Form Responses will start filling on the Form Response tab from Row 1. All Form Workflow Plus archived Requests will be on the archived tab on your spreadsheet and the dashboard.
Link your Google Form to a new spreadsheet
If you don't want to keep old requests on the same spreadsheet on the dashboard, please link your Google Form to a new spreadsheet. A new spreadsheet will be created on the dashboard for all new requests.