Supposing you have 50 tables without identity column, adding identity manually in the table designer would take you so much time. Here's a script to automatically add identity to a column.

List all tables without identity column.

SELECT 

(SCHEMA_NAME(schema_id) + '.' + name) as SchemaTable

FROM sys.tables

WHERE [name] NOT IN

(

SELECT 

OBJECT_NAME(OBJECT_ID) AS TABLENAME

FROM SYS.IDENTITY_COLUMNS

)

ORDER BY SchemaTable;

GO

Add identity

DECLARE cur CURSOR FOR 

select   

a.TABLE_SCHEMA as sn, 

a.table_name as tn, 

a.column_name as cn 

from information_schema.columns as a

inner join sys.tables as b on a.table_Name = b.name

where table_schema in(schema names) and  

ordinal_position <= 1 and 

table_name NOT IN(SELECT OBJECT_NAME(OBJECT_ID) AS TABLENAME   FROM SYS.IDENTITY_COLUMNS)and 

substring(a.column_name, len(column_name)-1, 2) = 'Id' 

DECLARE @sn sysname,

@tn sysname, 

@cn sysname, 

@sql varchar(500) 

OPEN cur     

FETCH NEXT FROM cur INTO @sn, @tn, @cn 

WHILE @@FETCH_STATUS = 0     

BEGIN 

SET @sql = 'ALTER TABLE [' + @sn + '].['+ @tn +'] ADD ' + @tn +' int NOT NULL IDENTITY (1,1)'    

PRINT @sql   

exec (@sql)  

FETCH NEXT FROM cur INTO @sn, @tn, @cn     

END 

CLOSE cur     

DEALLOCATE cur

Happy coding :)