When reporting a first conditional, the following tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses. changes may be applied.

"If we leave now, we’ll catch the train."
I told him that if we leave now, we’ll catch the train. (if we can still catch the train)
I told him that if we left, we’d catch the train. (if the train has already left)

Note that the verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis. left in the last sentence is in the real past simple tense.

Zero conditional in indirect speech
Conditional and IF-sentences in indirect speech Second conditional in indirect speech