Retroactively assign a user to a Parent account when using the Sponsored Members Add On.

pmpro-sponsored-members-assign-to-parent.php

/**
 * Retroactively assign a user to a Parent account when using the Sponsored Members Add On.
 * Enter the user ID of parent account in the "Assign to Parent Account" on the "Edit Profile" screen. 
 * 
 * Note: The user's active Membership Level must be the correct "Child" level for that Parent/Child relationship.
 *
*/
function pmprosm_assign_child_members( $profileuser ) {

	if ( function_exists( 'pmprosm_getSponsor' ) && current_user_can( 'edit_users' ) ) {
		
		// Get the parent for this user.
		$parent = pmprosm_getSponsor( $profileuser->ID );
		if ( ! empty( $parent ) ) {
			$parent_id = $parent->ID;
		} else {
			$parent_id = '';
		}

		// Show the field to update the parent for this user.
		if ( empty( $parent_id ) ) { ?>
			<table class="form-table">
				<tr>
					<th>
						<label for="assign_child_member"><?php _e('Assign to Parent Account'); ?></label>
					</th>
					<td>
						<input type="text" value="<?php echo $parent_id; ?>" name="assign_child_member" id="assign_child_member" />
						<p class="description">Enter the Parent Account's user ID for this user.</p>
					</td>
				</tr>
			</table>
			<?php
		}
	}
}
add_action( 'show_user_profile', 'pmprosm_assign_child_members', 20, 1 );
add_action( 'edit_user_profile', 'pmprosm_assign_child_members', 20, 1 );

function pmprosm_profile_assign_child_members( $user_id, $old_user_data ) {
	if ( isset( $_POST[ 'assign_child_member' ] ) && (int)( $_POST[ 'assign_child_member' ] ) ) {
		
		// Get the vars.
		$parent_id = $_POST[ 'assign_child_member' ];
		$sponsored_code = pmprosm_getCodeByUserID( $parent_id );
		$membership_level_id = (int)$_POST[ 'membership_level' ];

		// Check that the user has a child level.
		if ( pmprosm_isSponsoredLevel( $membership_level_id ) ) {
			// Set their new membership level and assign their sponsor.
			pmprosm_changeMembershipLevelWithCode( $membership_level_id, $user_id, $sponsored_code );
			pmprosm_addDiscountCodeUse( $user_id, $membership_level_id, $sponsored_code );
		}
	}
}
add_action( 'profile_update', 'pmprosm_profile_assign_child_members', 10, 2 );

This recipe is included in the blog post on "Assign a “Parent” Account to an Existing User or Member: Sponsored Members Add On Recipe" at Paid Memberships Pro here: https://www.paidmembershipspro.com/assign-parent-to-user-sponsored-members-add-on-recipe/