I hope this helps and is what you were looking for.
Answered with a tutorial: https://grabcad.com/tutorials/how-to-remove-the-part-in-solid-works
AttachmentsFlanged Strainer 2.SLDPRT, 278 KB
Stephen Nyberg is right - a much cleaner model. The remodel is better than my fix - but you did ask how to remove / fix your current model.
The easiest way to remove the "surface"; add a cut revolve based on a converted sketch (the one used to produce the protrusion).
Attachmentsflanged strainer_Mod.SLDPRT, 431 KB
thanks for the valuable reply sir
Another way It can be done is with a cut revolve and delete body.
Answered with a tutorial: https://grabcad.com/tutorials/how-to-remove-the-part-in-solid-works--1
Try this : Click under sketch > 3D sketch
Then click 'Convert Entities' and click the edges surrounding the area you want to remove. Once done, exit the sketch. Click 'Extruded cut' and select a plane almost parallel to the portion you want to remove. Enter a desired height and hit the checkmark. It should be gone. Let me know if it worked.
Well, I cannt open the file since this is a future version Solidworks so that I can try it but have you tried this:
Got to Command Line - Insert - Cut - Boundary (or "With surface")
Sir check it
Attachmentsflanged strainer.SLDPRT, 864 KB
Looks good. That was my first approach with your model but I didn't like the way cut left some small geometry that could cause problems. Also sketch 2 and 28 are under-defined and I think the shell feature results with a better interior fillet. the joint of the two parts does not have a uniform thickness.