“If you wish to withdraw your I-539 application, you must upload your request to your myUSCIS account. Make sure to include the reason for your withdrawal and an original signature with your request.
Please note, withdrawal requests are voluntary and cannot be reopened.
It is USCIS policy not to issue refunds unless USCIS solicited the fee in error. Filing fees and fingerprinting service fees are non-refundable.
However, if you applied for an extension of stay and you leave the United States before a decision is made on your application and you plan to return to the United States in the future, please keep a copy of your application plus the receipt notice to show to the Immigration Inspector on your return travel to the United States. Otherwise, you may be denied entry for overstaying on your last visit.”