Add a level dropdown at the top and bottom of the users table view than add support to bulk add level memberships to users.

bulk_level_change.php

<?php
/**
 *
 * Add a  level dropdown  at the top and bottom of the users table view than add support to bulk 
 * add level memberships to users. Use at your own risk. Users can expect timeouts and rate limiting often 
 * when bulk editing even a relatively small number of members depending on their hosting and how things are wired up.
 * link: TBD
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 * 
 */
function pmpro_display_level_selection_for_bulk_users( $which ) {

		// The attributes need to be different for top and bottom of the table.
		$id     = 'bottom' === $which ? 'pmpro_bulk_change_level2' : 'pmpro_bulk_change_level';
		$submit = 'bottom' === $which ? 'pmpro_bulk_change_level_submit2' : 'pmpro_bulk_change_level_submit';

		?>
		
		<div class="alignleft actions">
			<label class="screen-reader-text" for="<?php echo esc_attr( $id ); ?>">
				<?php esc_html_e( 'Change level', 'paid-memberships-pro' ); ?>
			</label>
			<select id="<?php echo esc_attr( $id ); ?>" name="<?php echo esc_attr( $id ); ?>">
				<option value<?php echo esc_attr(""); ?>>-- <?php esc_html_e( 'Choose Level', 'paid-memberships-pro' );?> --</option>
				<?php
				$levels = pmpro_getAllLevels();
				foreach ( $levels as $level ) {
						?>
					<option value="<?php echo esc_attr( $level->id ) ?>"><?php esc_html( $level->name ) ?></option>
					<?php
				}
				?>
			</select>
			<input type="submit" name="<?php echo esc_attr( $submit ); ?>" id="<?php echo esc_attr( $submit ); ?>" class="button" value="<?php echo esc_attr( 'Change' ); ?>">
		</div>

	<?php
	}
	add_action( 'manage_users_extra_tablenav', 'pmpro_display_level_selection_for_bulk_users', 20, 1 );





	/**
	 * Process bulk change level.
	 */
	function pmpro_bulk_change_level() {
		if( empty( $_GET['pmpro_bulk_change_level'] ) && empty( $_GET['pmpro_bulk_change_level2'] ) ) {
			return;
		}
		if( empty( $_GET['users'] ) ) {
			return;
		}

		$user_ids = array_map( 'sanitize_text_field', ( $_GET['users'] ) );
		$level_bottom = sanitize_text_field( $_GET['pmpro_bulk_change_level2'] );
		$level_top = sanitize_text_field( $_GET['pmpro_bulk_change_level'] );
		$level = $level_bottom !== "-- Choose Level --" ? $level_bottom : $level_top;

		//loop users and change level
		foreach( $user_ids  as $user_id ) {
			pmpro_changeMembershipLevel ( $level, $user_id );
		}
	}

	// Hook into users table screen to process bulk change level.
	add_action( 'admin_head-users.php', 'pmpro_bulk_change_level' );