They are designed the same as military Mauser BA rifles floorplates: depress the button inside the hole at the rear/central part of the floorplate and slide the floorplate forward (towards the muzzle) while holding the button depressed. (GI's used a bullet nose)
About 1/8" movement should be enough for the floorplate lugs to disengage with the bottom metal lugs, and drop out into your hand, along with the magazine spring & follower.
Re-assemble in reverse order. .
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