How Do I Create Custom User Role When a User Registers on WordPress in PHP?

My question is "How do I assign a custom user role when a user selects a specific checkbox when registering for an account?"

There is two options: Option 1: Contractor Option 2: Vendor

Registration Flow: #1 User Registers -> Checks either Contractor or Vendor -> Account Created & Assigned a specific user role based on which option they checked.

So far I have the code to create the user flow but I am not sure what conditional logic needs to be added to the additional function.

function contractor_role() {  
 
    //add the contractor user role
    add_role(
        'Contractor',
        'Contractor',
        array(
            'read'         => true,
            'delete_posts' => false
        )
    );
 
}
add_action('admin_init', 'contractor_role');

function vendor_role() {  
 
    //add the vendor user role
    add_role(
        'Vendor',
        'Vendor',
        array(
            'read'         => true,
            'delete_posts' => false
        )
    );
 
}
add_action('admin_init', 'vendor_role');