Change “logged in” link in (you must be logged in to post a comment)

To change the login link only in this template, replace the wp_login_url() function call with your login link:

'must_log_in' => '<p class="must-log-in">' . sprintf(
    /* translators: %s: login URL */
    __( 'You must be <a href="https://wordpress.stackexchange.com/questions/258398/%s">logged in</a> to post a comment.' ),
    "https://yourdomain.com/my-account"
    ) . '</p>',

If you want to generally redirect users to another url if they need to log in, it is better to use the filter login_url:

function wpse_258398_login_url ( $login_url, $redirect, $force_reauth ) {
    return "https://yourdomain.com/my-account";
}
add_filter( 'login_url', 'wpse_258398_login_url', 10, 3);

Be aware though, this will affect all redirects to login. Even when you are redirected to login for the admin backend.