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If I understand your question correctly, you want to delete previous month's submission data from your form. Is that correct?
You may like to take a look at the following guide which should explain you all the options available to delete submissions: https://www.jotform.com/help/377-How-to-Delete-Form-Submission-Data
Please check point #6, 7 & 8 on how to delete submission based on a date range.
Hope this helps.
Do get back to us if you have any questions.