You'll need more than just a case knife if you don't want to repeat the marks already there.
<from an old post of mine>
WARNING!
If you are technically inept or have Homer Simpson coordination, read no further, take it to a trusted watchmaker.
1. Remove the bracelet first.
2. Get a small block of soft wood and drill a 10mm hole big enough to sit the crown in.
3. Hold the watch upright on the wood with your left hand with the crown in the hole.
4. Use a Gem razor blade* and gently insert it into the seam opposite the crown.
5. Use a gentle seesaw movement to work the blade into the seam and slowly move around the top part of the case.
WARNING - DON'T PRY....ever.... (as stipulated by a professional watchmaker
@Archer )
6. When you see a gap opening, get a case knife or even a fine table knife and continue to work the gap.
It should start to open from the top side and you can use a thicker blade to pop it off.
Good Luck with it.
Cheers
Jim
*
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