When reporting a zero 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.

Present timeA concept which is related to our perception of reality; that part of existence which is measured in seconds, minutes, hours, days, weeks, etc.

"If John is cursing, it means that he is very angry."
She said (that) if John is cursing, it means that he is very angry. (if this is a general truth)
She said if John was cursing, it meant that he was very angry. (if this refers to a past habit; John may have changed or died since then)

Past time

"Julie walked the streets without an umbrella if it was raining."
It was rumoured that Julie had walked the streets without an umbrella if it was raining.

Here only the tense in the main clauseA clause that could be a sentence in itself. E.g.: I wouldn’t go there if I were you. ("I wouldn't go there") When I arrived he was surfing. ("he was surfing") changes. No changes are made in the if-clause as it does not express a condition but functions as a time clause.

Conditional and IF-sentences in indirect speech
Conditional and IF-sentences in indirect speech First conditional in indirect speech