1. Copy allinstructors.php file from parent WPLMS theme into your child theme.
this would ensure that WP loads the template from child theme instead of parent theme and your changes are safe from theme updates.
2. Edit the allinstructors.php file in the child theme.
3. Paste this code in allinstructors.php
https://gist.github.com/MrVibe/91a79b2b108653ac0646
The above example assumes custom role you want to include in all instructors is “editor”, you can change it or append it according to your needs.