Preview button in Blog uses wrong link

Hi

When writing a blog post, I see there is now a preview button - great idea.

The problem is that it needs to go to: sitename/myfolder/myfile.php?s=blah

but instead it goes to: sitename/blog/post.php?s=blah

How do I change the path so that the preview works (changing the site folder and file names isn't an option).

Cheers - Mark

Health check

    PHP 5.6.32 is up to date
    MySQL 10.0.31-MariaDB-cll-lve is up to date
    Image processing available

Summary information

    Perch: 3.0.11, PHP: 5.6.32, MySQL: 10.0.31-MariaDB, with PDO
    Server OS: Linux, litespeed
    Installed apps: content (3.0.11), assets (3.0.11), categories (3.0.11), perch_blog (5.6.1), perch_events (1.9.5), perch_gallery (2.8.9)
    App runtimes: <?php $apps_list = [ 'perch_blog', 'perch_events', 'perch_gallery', ]; ?>
    PERCH_LOGINPATH: /perch
    PERCH_PATH: /home/dasolcou/public_html/hamptonwick.org.uk/perch
    PERCH_CORE: /home/dasolcou/public_html/hamptonwick.org.uk/perch/core
    PERCH_RESFILEPATH: /home/dasolcou/public_html/hamptonwick.org.uk/perch/resources
    Image manipulation: GD
    PHP limits: Max upload 100M, Max POST 100M, Memory: 512M, Total max file upload: 100M
    F1: 3b606135b33e6a102526838f4152a807
    Resource folder writeable: Yes
    HTTP_HOST: www.hamptonwick.org.uk
    DOCUMENT_ROOT: /home/dasolcou/public_html/hamptonwick.org.uk
    REQUEST_URI: /perch/core/settings/diagnostics/
    SCRIPT_NAME: /perch/core/settings/diagnostics/index.php