actually it's a complex task.
- at first, you must be able to write some peace of code, at least to disassemble/assemble watch face file ("wf" below). you not required to be a super programmer, but ability to write little app you must have. of course editor with gui wold be more preffer
- you must separate frame (image) blocks (even without decoding for beginning), to understanding where it begins and where it finishes. not for each frame, but you must investigate a logic of a placement.
- you must find the pointers to frame blocks
- investigate structure of frame block descriptions
- now you may try to decode frames
- analyze header structure
- make a simple viewer for this format and try to use it for as many compatible wf'ses as it's possible, to be sure what you can read it all correctly
- try to make a writer and test your results
- polish the editor.