Question

Mohan said to Ram," please help my brother"

change into indirect speech

Answer 1

It is an imperative case. The quoted speech in such cases usually starts with the first or the base form of the verb. The reporting verb is usually converted into 'requested', 'advised', 'ordered', etc. depending upon the mood of the quoted speech. In such sentences the joining word 'that' is not used. 'To' is used while reporting the quoted speech. So the indirect speech of the question mentioned above is:

Mohan requested Ram to help his brother.