Please suggest what food should you not eat to avoid getting diverticulitis after you have allready had it?

High fiber diet. There is no proven way to prevent a recurrent attack of diverticulitis. The old rule of avoiding nuts and seeds has been disproven. My experience tells me that avoiding constipation and eating a high fiber diet (such as oatmeal) or taking fiber supplements every day (such as benefiber or metamucil) may prevent recurrent attacks, but there is no guarantee.
None. No study has demonstrated that any food is associated with causing diverticulitis. Enjoy whatever it is that you enjoy. If you're going to get a recurrence, you're going to get it. The food isn't going to be the culprit.