But I was wanting to roll back from Microsoft Edge "Beta" to the public release of Microsoft Edge.
What you want is not possible. The version of EdgeHTML on your system is directly linked to the build of Windows 10 you are using. Previous versions of Edge (i.e. EdgeHTML 15) cannot be used on current builds of Windows 10 (i.e. 1803). So this means you are stuck with EdgeHTML 18 if you have an RS5 Insider Preview build installed.
How can I do this?
Reinstall Windows and install 1709 and/or 1803 allowing which will allow you to use EdgeHTML 16 (1709) or EdgeHTML 17 (1803).