How to sort the filter

Hello,

Foolowing your answer on a previous post, I’ve integrated this shortcode in my page. [publishpress_authors_list layout=”authors_index” group_by=”last_name”]

The authors are now sorted properly. BUT the filter on the top of my page is now not sorted anymore, I have B M Q C because the filter order is still based on the first name and not the name.

How can I fix this, knowing that I would like if possible, to continue displaying Firstname LASTNAME but sorted by last name.

Any way of achieving this goal?

Tx a lot,

Marine

The page I need help with: [log in to see the link]