As Michael mentioned in early comment, your are trying to perform an upgrade with the wrong process.
Firstly we have to be clear about update and upgrade.
Update
Sometimes called a software patch, an update is an addition to the current version of the application, operating system, or software that you are running. A software update addresses any issues or bugs to provide a better experience of working with the technology. In RHEL, an update relates to a minor release, for example, updating from RHEL 8.1 to 8.2.
Upgrade
An upgrade is when you replace the application, operating system, or software that you are currently running with a newer version. Typically, you first back up your data according to instructions from Red Hat. When you upgrade RHEL, you have two options:
In-place upgrade: During an in-place upgrade, you replace the earlier version with the new version without removing the earlier version first. The installed applications and utilities, along with the configurations and preferences, are incorporated into the new version.
Clean install: A clean install removes all traces of the previously installed operating system, system data, configurations, and applications and installs the latest version of the operating system. A clean install is ideal if you do not need any of the previous data or applications on your systems or if you are developing a new project that does not rely on prior builds.
As you are trying to move from version 7 to version 8 you need an upgrade.
In this point I would like to share with you the next video from Red Hat channel in youtube, this video shows you the In-Place Upgrade using Leapp.
Let me know if this resolve your concerns,