Apply another template, theme (other than built-in) to the current presentation

If you want to apply a theme or template that is not in the themes gallery on the Design tab you can use an option that is called 'Browse for themes.
Here's a sample presentation with a custom theme applied to it. We want to apply another theme to that presentation that is not in the themes gallery.

Click on the 'More' button in the themes group. Then choose Browse for themes.

Navigate to the folder where your template or theme is situated. Select it and click Apply.

This is the result: