I want to replace my I phone 7 plus’s batterry

You have to make an appointment first with a genius at any Apple Store.

I'd say it takes less than 90 min.

Don't forget to back up your phone before you take it to the store.

And turn off "Find my iPhone" feature.

Your cost will be zero if your phone is still under warranty, or ¥3,200 otherwise.

iPhone のバッテリーと電源 - Apple サポート 公式サイト

予約必須。

1時間未満。