Link to the parent post in attachment page

Here’s one way within the main loop on the attachment’s page:

First we get the parent ID from the current attachment’s post:

$parent_id = get_post_field( 'post_parent' );

Then we check if it’s non-zero and print the link to the parent:

if ( $parent_id ) {
    printf(
        '<a href="https://wordpress.stackexchange.com/questions/312468/%1$s">%2$s</a>',
        esc_url( get_permalink( $parent_id ) ),
        esc_html__( 'Go to parent', 'wpse' )
    );
}

Hope you can expand this to your needs!