For user base limit
$total_submission = get_post_meta( $form_id, 'wpadcf7sl-total-submission', true );
$total_count = get_user_meta( $user_id, "wpadcf7sl-total-submission-{$form_id}", true );
$remaining = $total_submission - (int) $total_count;
For form base limit
$total_submission = get_post_meta( $form_id, 'wpadcf7sl-total-submission', true );
$total_count = get_post_meta( $form_id, 'submission-total-count', true );
$remaining = $total_submission - (int) $total_count;
Above are given how to calculate the remaining limit.