Applying a Branded Template Theme over an Old Google Slides Presentation

Your organization may have a very distinct brand which is a result of the hard work put in by members of your marketing team, and it is likely mandatory. How do you apply that branding to an old presentation?
For Google Slides presentations, especially those intended for outside parties, you may want to use the branded theme from a template made available by your organization's Google Workspace administrators.
If you wish to apply the theme in that template to an existing slideshow, you will first have to create a new presentation from the template, and then import the theme from that template into the old show. Unfortunately, Google has not given Workspace admin's the ability to add themes by themselves; only themes to templates. Therefore, this is a two step process. (Are you listening, Google?)
Click below for Google's official instructions on this process. However, if those don't supply enough detail, then this video is for you!
support.google....