In order to participate in our tenders, you should write a request letter. you can do it when it is confirmed by our manager. The letter should have been addressed to our manager rather than me.
What I didn't mention in the sentences is that applicant had addressed the letter to me while it should have been done to the manager.
So, "should have been addressed" is correct. Isn't it?
The way you propose is confusing; mixing tenses. You have to decide if 1) you're giving directions, or 2) you're recounting what's happened. Obviously you can start with 2) and then go to 1) directions as to how to remedy.
