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I'm not sure that you can get rid of the flaw on your Previewing screen, to be frank. At least, not by yourself.
The camera you have apparently has, internally, a separate optic arrangement for the preview screen's view... this is shown by the blob not showing up nor obscuring the photos ( - you say, it's not on saved files or prints, but is it showing up on the newly taken photos? if so, then it might not be on separate optics, and might be on the lens, so check the lens for dirt or dust in that case.)
Some of the more expensive camera have a 'cleaning' function, that shakes dust off the internal optics. Yours presumably does not.
Since the dirt or other problem that causes the blob is internal to the camera (given that it does not show up in newly taken photos as printed out or as viewed on the computer) you would have to disassemble the camera to have a hope of fixing it yourself. That requires special tools and expertise.
You have basically the choices of tolerating the problem (??) or having the camera serviced, or replacing it, I think.
To have it serviced, go tohttps://camerarepair.fujifilm.co.uk/
(If you are replacing it, you might doubtfully get something for the old camera on gazelle.com.)