Change roles for new PMPro members to custom roles at checkout based on level. Add this code to your active theme's functions.php or a custom plugin.

pmpro-change-role-custom-roles.php

<?php
/*
	This code assumes you already have custom roles created
	for bronzemember, silvermember, and goldmember.
	Members signing up for membership level #1 get "Bronze Member" role.
	Members signing up for membership level #2 get "Silver Member" role.
	Members signing up for membership level #3 get "Gold Member" role.
	Members cancelling are given the subscriber role.
	Admin users are ignored.
*/
function my_pmpro_after_change_membership_level($level_id, $user_id)
{
	//get user object
	$wp_user_object = new WP_User($user_id);
  
	//ignore admins
	if(in_array("administrator", $wp_user_object->roles))
		return;

	if($level_id == 1)
	{
		//New member of level #1. Give them Bronze Member role.
		$wp_user_object->set_role('bronzemember');
	}
	elseif($level_id == 2)
	{
		//New member of level #2. Give them Silver Member role.
		$wp_user_object->set_role('silvermember');
	}
	elseif($level_id == 3)
	{
		//New member of level #3. Give them Gold Member role.
		$wp_user_object->set_role('goldmember');
	}
	elseif($level_id == 0)
	{
		//Cancelling. Give them Subscriber role.
		$wp_user_object->set_role('subscriber');
	}
}
add_action("pmpro_after_change_membership_level", "my_pmpro_after_change_membership_level", 10, 2);
?>

This recipe is included in the blog post on "Give New Members Author Role" at Paid Memberships Pro here: https://www.paidmembershipspro.com/give-new-members-author-role/