how can i downgrade back to iOS 10 on my iphone 7 plus?

Downgrading is not supported.

What troubleshooting steps have you taken?

See this article for specifcs regarding the screen:

Get help with the display on your iPhone, iPad, or iPod touch - Apple Support

You may also want to think about backing up your phone and restoring it:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Gooodman wrote:

I need to downgrade to ios10 pls help me ios 11 *****

Did you read the thread before posting in it? I think not because, if you had, you'd understand that you can't do what you want.

Hi, Unfortunately you can no longer downgrade back to iOS as apple have signed the software, however try restoring the phones software using iTunes on a computer. if this does not work i would recommend taking it to the apple store.

best wishes in resolving your case.

Ben

You cannot go back to iOS10, only 11.0.3.

I need to downgrade to ios10 pls help me ios 11 *****