Delete submissions within a specific time range

How can I delete all submissions from all forms within a certain date period with only 1 click?

You can select a time frame from submissions page by clicking the gear icon, and click Delete submissions in the table menu from the same page. 

I want to do ALL forms not just 1 form at a time

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You can only deleted submissions form by form.

The only way to remove all submissions from several forms at the same time would be to clone each form and then delete all of them.

I would however personally suggest only deleting the submissions from one form at a time to avoid removing anything that you would like to keep.

Do note that once removed it is not possible to restore the data back.