I want more storage off may iPhone 7 Plus

You cannot get more storage on any iPhone. Each Apple device comes with a set amount of storage that cannot be changed. You have two options:

• Buy a new iPhone that offers more storage, or

• Optimize the storage on your current iPhone. You can do this and possibly free up space, by deleting apps, deleting old photos you no longer need, old emails & messages. You can read more about it here: How to check the storage on your iPhone and iPad - Apple Support