To make changes to fields, or to add or remove fields, you can use functions and/or filters inside a functionality plugin:
https://wpjobmanager.com/document/editing-job-submission-fields/
https://css-tricks.com/wordpress-functionality-plugins/
Here’s an example tutorial:
https://wpjobmanager.com/document/tutorial-adding-a-salary-field-for-jobs/
You could also use a third-party plugin such as WP Job Manager Field Editor:
https://plugins.smyl.es/wp-job-manager-field-editor/
… which has a nice GUI for editing fields.
However, we aren’t able to help with custom code requests like this. ?? You may want to look into one of these services for help:
https://codeable.io/
https://studio.envato.com/
https://jobs.wordpress.net/
Sorry I can’t be of more help here!
