Question

"thank you very much" I said to the stranger . convert into direct speech

Answer 1

qstn is wrong
it is already in direct speech.
I said to the stranger,"Thank you very much".
we have to convert it into indirect speech
I thanked the stranger very much.

Answer 2

“Thank you very much”, I said to the stranger.

This sentence is written in the direct speech.

When a direct speech is converted into an indirect speech, some changes are made, but the meaning is not altered.

The statement should imply the same as it did before.

So, the indirect speech conversion of the given sentence will be, ‘I thanked the stranger.’.