Student or Learner
I need to know how to use re expressing regrets wiht should have, maybe Have one rule or something?
Your question is difficult to understand. Do you mean, how do I use 'should have' in a sentence to show regret?
I am sorry I didn't come on Thursday. I should have rung to tell you I wasn't able to come.
Yes, you should have rung to tell me you were not coming.