How to delete the message on inbox?

I assume you are referring to the Inbox button beside the form in the My Forms page? Please allow me to inform you that it is not possible to delete the submission from the inbox.

If you want to delete a submission, you will have to do it from the form's submissions page. To go to your form's submissions page and delete a submission, please follow our guide here: How to Delete Form Submission Data.

If you need further assistance or if you are referring to a different concern, please do let us know.
Regards.