I need to know how to set Licence in purchased WordPress theme,
Thanks for asking your question at Envato Forum.
How to contact any Item Author from Here
If they ask about purchase key then collect from Here
How to Install Your ThemeForest WordPress Theme
Still have any question open a Envato help ticket from Here
After installation the theme you have to activate the license through your site dashboard. Please check theme documentation hope you will get proper help there.
Otherwise The best way to get this answer is Contact your purchased Theme Author.