bank of america app... can't open

That model number relates to an iPhone 6s, is that right?

An iPhone 6s can run iOS 11, 12 and 13 and will be able to get iOS 14 when that is released by Apple in the fall.

So to get the Bank Of America app to work, you need to upgrade your phone to a newer iOS. There is no other way to get it to work. If you stay on iOS 10 then the app will never work.

Info about upgrading - Update your iPhone, iPad, or iPod touch - Apple Support

Talk to BoA customer support.

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2.8; iPad Air 2, ipadOS 13.6.1; iPhone 8+, iOS 13.6.1; TV 4th Gen, tvOS 13.4.8;  HomePods, audioOS 13.4.8 and Airport Express w/ Airplay 2

So the Bank of America app requires iOS 11.0 or later

So if your running an iPhone with 10.3.3, the app won't work.

I ask again, which device? As iPhone isnt really helpful as there is so many.

It may be your phone is to old to get iOS 11 or you need to do a software upgrade

No worries.

Glad I could help

what device? what iOS?