child theme functions.php not overriding plugins

Hello!

I am new, so bear with my probably obvious mistakes.
I have a child theme installed, and I am trying to override wpjobmanager-resume-manager fields using this guide:

https://wpjobmanager.com/document/resume-manager-editing-submission-fields/

Adding the code snippets to the functions.php doesn’t change anything at all. Have I misunderstood something? Is there a need to override the wpjobmanager functions.php instead of the top-level theme’s functions.php, or do I miss some refference code?