Black strip at bottom screen after battery replacement

Now, I have a black strip at the bottom of my iPhone 4S screen which has appeared after I replaced the battery. This black strip covers about 1/4 th of the bottom-most row of icons. Other than that the phone works perfectly fine including the touch response from icons which are partially covered. iOs installed version 9.3.5 (13G36)

iPhone 4S battery replacement does not require screen removal at all. All that has to be done is to unscrew two screws next to the charging cable input port near the home button and slide out the back cover to access the battery. Unscrewing two more screws before disconnecting the battery connector is all that is needed to be done further.

For Ben - I found it quite easy to pry out the battery as it was not held too firmly unlike what I had experienced during battery replacement in the older iPhone models. I therefore can not really figure out as to why and how the screen could have got damaged. As stated earlier, the phone works absolutely fine with even partially obscured icons responding to the touch as normal. Thanks for your responses. I hope we can figure out the solution soon.

I have the photo but don’t know as to how to attach it here.