1. you need to get NOC From your company - stating that the company has no objection to do so.
2. you need your original Engineering degree certificates with proper attestation.
3. make the new contract with prescribed format stating your new profession.and signed by you and your sponsor

4. take all the above said documents + your original pasport & QID
submit all with Immigration Dept, they will do the changes

and the charges may be Aroung Qr.300/- for the same.