Hi @creation,
Unfortunately by default there is no option to display messages in DESC order. Buddypress private messages is supposed to be like a chat which is why the latest is displayed last.
Please note that this issue is related with the customization of a third party plugin (BuddyPress), not with the use of your theme. As theme authors, the installation, setting or debugging of third party plugins isn’t part of the support we will provide.
To go further, we invite you to ask for more help from the plugin authors and post your request on their support forums:
https://buddypress.org/support/
We remain available for all support requests related with the use of your theme.
Regards,