Luminar AI - Using Preset & Custom Aspect Ratios

Luminar has a dedicated tool to enable you to alter the aspect ratio of your photographs.

Step 1 - Head over to the Edit Tools, then scroll to the Composition AI tool in the Essentials panel.

Step 2 - Using the pull-down menu next to the Ratio option, select the aspect ratio you want.  Or you can select Free to manually create an aspect ratio you want.

Step 3 - Using the grid handles around your image to scale the crop to your requirements.