すみません、これを温めてもらえますか？ — Excuse me, could you please warm this up for me? (Convenience · Store, Formal — to staff, JLPT N4)

Gesture & etiquette

Hold up the specific item to be heated.

While it's generally okay to ask, some items are not meant to be heated (e.g., certain salads, fresh fruit). Be prepared for a polite refusal if the item isn't suitable for microwaving.