Check this tutorial:
There is no problem you have no header line in source file - ODI allows you to setup the names of the colums.
In my txt file not having column names, having only data which is TAB delimited. Please see my example. In my target table having column names how to do mapping?. Please let me know.
Check the tutorial I have provided.
On step "1.5 Defining Source Designer Model" you setup the file as "Delimited", no header.
When reverse engineering, ODI will suggest the columns named C1, C2, C3.....
But you may rename the columns.
Then follow up the rest of the tutorial.