Both are correct, but they mean very different things (if sentence 2 is meant to say 'had been submitted...')
The first means that I found this news out, and I found it out on the 28th. In other words the tender may have been submitted five days ago or five years ago!- but *I* found out on the 28th.
The second means that the *event ITSELF* took place on the 28th: in other words whoever submitted the tender did so on the 28th.