When I hear or read "have an apple" I understand this is an invitation (imperative), to be translated in French by "prends une pomme" or "prenez une pomme".
In French the imperative with "have" would be "Aie une pomme"
The subjunctive form is "Que tu aies une pomme" (sing) or "Que vous ayez une pomme" (polite sing and plural)