The indirect form of the sentence "He said to me, 'You had better take an umbrella, it is raining heavily." is-

He advised me to take an umbrella as it was raining heavily

He told me better for taking an umbrella as it was raining heavily

He advised me to take an umbrella and it was raining heavily

As it is raining beavily, he told me to take an umbrella

As it was raining heavily, he adivised me for taking an umbrella