Indirect Speech: no tense changes
the reporting verb is in a present tense;
Joanna: I have just arrived in Hanoi.
Joanna says she has just arrived in Hanoi. (reporting a recent telephone conversation; the reporting verb say is present simple)
the reported words are true at the time of reporting:
George: I'm meeting Karen tomorrow.
George said he is meeting Karen tomorrow. (reported on the same day, tomorrow still refers to tomorrow)
the reported words express a general truth:
Copernicus: The planets revolve around the sun.
Copernicus stated that the planets revolve around the sun. (it is a general truth)
the reported words refer to an unreal situation:
Mike: I wish I was a year older; then I could enter the race.
Mike wished he was a year older, so he could enter the race. (he is not older)