Whenever I try to search BDO [Black Desert Online] sea I get no result, can only see other versions which is restricted in SEA region. How to download or find BDO sea on Steam?

Hi there, make sure your "Steam Region" are in somewhere that count in SEA region, e.g. Singapore, Malaysia, Indonesia. 

You may view and change your store region from your Account Details page.

If it's still doesn't work, I recommend you to submit a ticket here

Hope it helps, cheers!