Source code for https://formidable-masterminds.com/change-wordpress-user-role-when-editing-field-in-a-view

frm_after_update_entry.php

<?php

add_action('frm_after_update_entry', 'update_user_role', 10, 2);
function update_user_role($entry_id, $form_id){
    if ( $form_id == 4 ) {

        $userid = $_POST['item_meta'][15];// ID of the userID field
        $role = $_POST['item_meta'][19];// ID of the role field
            
        if ( $userid && $role ) {
            $user = get_userdata( $userid );
            if ( $user && ! $user->has_cap('administrator') ) {
                $user->set_role( $role );
            }
        }
    }
}

frm_trigger_entry_update.php

<?php

add_action('frm_after_update_field', 'frm_trigger_entry_update');
function frm_trigger_entry_update($atts){
	$userid_field= '15';
	$entry = FrmEntry::getOne( $atts['entry_id'], true );
	$userid = FrmEntryMeta::get_meta_value( $entry, $userid_field );
	$role = $atts['value'];
	if ( $userid && $role ) {
		update_wordpress_user_role( $userid, $role );
	}
	$form = FrmForm::getOne( $entry->form_id );

	FrmFormActionsController::trigger_actions('update', $form, $entry, 'email');
}

update_user_role.php

<?php

add_action('frm_after_update_entry', 'update_user_role', 10, 2);
function update_user_role($entry_id, $form_id){
    if ( $form_id == 4 ) {

        $userid = $_POST['item_meta'][15];// ID of the userID field
        $role = $_POST['item_meta'][19];// ID of the role field

        if ( $userid && $role ) {
            update_wordpress_user_role( $userid, $role );
        }
    }
}

update_wordpress_user_role.php

<?php

function update_wordpress_user_role( $userid, $role ) {
	$user = get_userdata( $userid );
	if ( $user && ! $user->has_cap('administrator') ) {
		$user->set_role( $role );
	}
}