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

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.

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.

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