Modify Doogee S80 Phone Case STL with Custom Hand Loop

I have a Doogee S80 phone and a 3D model of its case (STL file available on Thingiverse: https://www.thingiverse.com/thing:3231543). I need a freelancer to modify the case to include a custom ergonomic hand loop and extend one edge.
Requirements:
Extend one edge of the phone case by 4 cm.
Design and integrate a hand loop:
Runs from the top left extended edge to the bottom right edge.
4.5 cm clearance from the body of the case to fit the hand comfortably.
12 cm usable width for hand placement.
Ideally S-shaped to avoid obstructing the camera.
Include a reinforced aperture/hole at the lower section of the handhold for attaching a keyring or chain.
Ensure the design is 3D-print ready and structurally strong.
Deliverables:
Modified STL file ready for 3D printing.
Optional: Preview render for approval before final delivery.
Skills Required:
CAD/3D modelling experience (Fusion 360, SolidWorks, TinkerCAD, or similar).
Experience with custom 3D modifications and 3D printing optimization.
Attention to detail and precision to ensure proper fit and function.
Budget: £20 (fixed price)
Deadline: ASAP
Additional Notes:
I’d like the freelancer to start immediately. Clear communication and fast delivery are important as I plan to print the model as soon as possible.