HP6236B Triple Output Volt meter replacement

[eribla]

Hi

I would like to replace the Volt meter instrument in my HP HP6236B power supply, but a can't find a way to unlock it from the front plate without
raw force and possibly braking it. (I still hope I can fix it, as it is "just sticking").

Anybody know the trick?? I can provide pictures if needed.

THANKS!!!!