Hello yamant,
There are instructions on how to do this when you go to Extensions > Template > JA Halite and view the parameter Page Layouts Overwrite.
You need the itemID for the article you want to assign a specific layout out to and then you just do this in the box provided: itemid=layout_name.
Article 1 Layout : left-right-body becomes:
1=left-right-body
2=right-body
(only one article id per row)
If you hover over the parameter name there is a tooltip with more detailed instructions.
I hope this helps 🙂
