Maybe it will work with another model?
There is no chance that CHDK complied for a different camera will work on yours. Sorry.
Nobody tested? I really need RAV.
Correct. Nobody tested using a different model's CHDK on an SX620. That's because the CHDK code needs to use exactly matched firmware addresses so needs to be compiled separately for each camera's firmware.
If you really need RAV badly, you will have to obtain a camera that has CHDK support. Or wait until someone volunteers to create a CHDK port for the SX620.