The red minus to change/remove build will not appear if you don't do this

To resolve the issue, select your app, navigate to the General section, and click App Review. Under Submissions, remove the current submission by clicking the red minus button. Next, go to the iOS App section and then to the iOS App Version area. Then scroll to build and when you hover over the build, a red minus button will appear—click it to remove the old build. Finally, add the new build.