Black spots in pictures?

Hi,

For the past few months I've had a prominent black spot in picture, particularly when using the middle (1x zoom) camera.

The other cameras are working as intended, no discolouration or black spots present.

I'm operating under the assumption this may be trapped dust underneath the actual cameras lense, since having taken the back off for a charging port replacement and back panel fix.

I was just wondering if there's any advice for repairing this, or any suggestions as to what it may be?

See below for picture.

Thanks in advance.

Adam.