You can  remove/add/modify input fields via filter hook as following.

Default input field index

keywords
job_category
companies
locations
salary_type
salary_range
job_status
job_type
job_level

Remove any input fields

function job_bm_filter_alert_input_fields_remove($input_fields){

  // To remove companies Job category input field
  unset($input_fields['job_category']);

  // To remove companies Companies input field
  unset($input_fields['companies']);

  return $input_fields;
}

add_filter('job_bm_filter_alert_input_fields', 'job_bm_filter_alert_input_fields_remove');

 

Change input field title

function job_bm_filter_alert_input_fields_remove($input_fields){


  // Change Companies title
  $input_fields['companies']['title'] = 'New Companies Title';

  // Change Companies title
  $input_fields['job_category']['title'] = 'New Job category Title';


  return $input_fields;
}

add_filter('job_bm_filter_alert_input_fields', 'job_bm_filter_alert_input_fields_remove');

 

Change input field details

function job_bm_filter_alert_input_fields_details($input_fields){


  // Change Companies details
  $input_fields['companies']['option_details'] = 'New Companies details';

  // Change Companies details
  $input_fields['job_category']['option_details'] = 'New Job category details';


  return $input_fields;
}

add_filter('job_bm_filter_alert_input_fields', 'job_bm_filter_alert_input_fields_details');