Prerequisites:
This page is nearly completely based on this blog post: https://j4ln.com/blog/unlocking-and-rooting-the-kyocera-digno-keitai-3-902kc/. It is highly recommended that you read the blog post, this page is a work in progress.
Before you can unlock the bootloader you will need to enable OEM unlocking and prepare the microSD card with a trigger file.
You will need to enable “OEM unlocking” in settings. This setting may be found under More settings > Developer options > OEM unlocking.