Cant sign into ITunes Store

im trying to update an app on AppStore on my iPhone 6s and it keeps asking me to sign into the iTunes Store using my Apple ID

so I keep entering my password and it says verification failed ,your Apple ID or password is incorrect

I’m not too sure what to do

I googled and the ITunes&App Store feature that’s supposed to be in my settings isn’t there

How can I sign into the ITunes store ?