If i (to know) that you were ill last week i (to go) to see you
If I had known that you were ill last week, I would have gone to see you.
Желаю удачи!
If I had known that you were ill last week, I would have gone to see you. (Если бы я знал, что ты болел на прошлой неделе, я бы пошел тебя проведать.)