How to use Customizable Borders -Lightroom Mobile 8.2.2 -

I don't know if there's a tutorial, but it's such a simple feature at the moment that it really doesn't need one:

1. Select an image, tap on the share icon, select "Add border and share...."

2. That opens the Border Options dialog which consists of three functions: Color, Thickness, and Border size, all of which are pretty simple to understand and control.

3. When done with the options, tap on the share icon (top right of the Border options box), then choose the export destination.

At this time, you have no control over the pixel size, quality, file-type, etc., these are all fixed, and nor can you add a watermark.