Adding a 5th icon to your dock bar

I'm new to this Iphone stuff, really new. I've had the phone for about 3 days!

I bought the phone second hand,.....it's a 6s Plus updated to iOS 12.1.4

With that said, I come from and android phone past and I would love to have more than just 4 icons on the dock bar (I think that's what it's called). The iphone won't let me add more than 4 SO, my question is this:

Is there any way to add another icon to the dock bar? whether by an app from the store or by a settings change on the phone?