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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.