I don't know if this is yours, but if it is, please contact us at this number.
If this is yours that you've misplaced, please don't hesitate to contact us here.
電話で伝言を残すときに↓
I don't know if this is yours,「あなたの物かわからりませんが」 but if it is,「でももしそうであれば」 please contact us at this number.「この電話番号でご連絡ください」
If this is yours that you've misplaced,「これがあなたが忘れ物をしたものでしたら」 please don't hesitate to contact us here at 000-0000-0000.「遠慮なくこちらに000-0000-0000お問い合わせください」