Currently, we are unable to edit the Booked/Sold to patron on a Group sale reservation once it has been created. You can edit the Contact of a group sale reservation using the steps here, however this does not reflect towards the sales order or Booked/Sold to field on the reservation.

If you need to change the Booked/Sold to patron on the reservation, before checking the group in you will cancel the reservations and create a new reservation with the correct patron. 

If you would like to see this become a future feature in Altru, please vote for this idea in the Community. We encourage you to vote on this post as this is an opportunity to have a voice in the product development process. Our Product Management team uses a variety of methods to determine new features in Altru, and the ideas in the Community is one way they do this, so your vote helps Product Management prioritize the new features that we put into the product.