Do you mean the clearance between the copper pour (polygon) and other copper, or between copper and the board edge? The board-edge clearance is already 0.3 mm; a separate polygon-to-copper clearance isn’t exposed in the board-edit controls.
Understood—you want 0.3 mm clearance between the copper pour and other copper. That setting isn’t exposed in the available board-edit controls, so I can’t apply it here. I’ve left the board unchanged; the existing 0.3 mm board-edge clearance is a separate setting.
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