The status of my paper which is in review since 3/02 is "A review is overdue. Two of 4 Assigned reviews are completed". I read in the journal site that review generally takes 1 month and the minimum number of reviews to make a decision by the editor is 2. The number of reviews is 2 since 1 March and the editor didn't make any decision? What should I do?
It's not true that just because your manuscript already has two reviews that the editor will make a decision. For example, maybe the two reviews disagree with each other, or one of the two reviews is poor and the editor is waiting for the third review as a tiebreaker. The third review is ten days overdue which is not a good sign, but you can't tell from the outside. For example, maybe the reviewer had emailed the editor saying the review will be late, and the editor is (sensibly) waiting as a result.
As for "what should I do", the answer is always the same. If you're concerned/impatient, write to the editor and ask what the status is. Otherwise just wait. The review process for your manuscript doesn't seem that long to me, so I would wait, but it's up to you.