@saurabh_aher if you're referring to an object i.e. a table I think you should be using backticks `` and not single quotes ''.  

However, based on the error message: concat('kdp_bronze_prod.salesforce.', outer(get_table.user_id)). 
I think in the concat function, it often helps to wrap a string in a LIT function. 

All the best,
BS