The back case of the watch contains an integrated rubberised o-ring.
Force is best applied by taking the band off and working at the edges adjacent to where the band meets the case.
There are small lips here where the thin metal Jimmy can be used to pry the case off with patience and low force by alternating between each end of the case.
The metal spudger tool recommded by this guide is the wrong tool for the job. The ends are far too thick.
Jimmy used: Jimmy