Rejected for exposure, please suggest

You won't be able to improve this picture as it contains multiple errors that are not to correct.

Washed out colours and missing sharpness is one of those:

This was probably the optimization software of your phone, because of the high noise level because your image is at ISO640.

Framing is a second one and yes, your picture is underexposed. You would need to get flashlight to lighten carefully the foreground to get a better exposure. If you do not have (semi-)professional equipment, you won't get this right.

If you get all right, you would need to produce a property release.