Will be held or would be held

No backshift. If we consider the direct speech: The instructor said,”The test will be held on March 20, 2021. Then we have to alter it into reported speech would offer the following:

1. The teacher stated that the test will be held on March 20, 2021.2.
The instructor said that the test would be held on March 20, 2021.
Which one is appropriate?

Both are correct.In sentence
1 the verb, “will” is not back moved. According to Cambridge dictionary, we don't need to change the tense if what is said is still true or appropriate or has actually not taken place yet. It can be reported in this way before March 20, 2021, i.e. before the test is held.

Sentence 2 “will” is back shifted to “would”. There is no limitation. We can backshift immediately after the words are spoken and likewise even after the examination is over.

When backshifting is not needed:.

Ref. Cambridge dictionary
No backshift.We do not require to change the tense in indirect speech if what a person stated is still true or appropriate or has actually not taken place yet. This frequently occurs when somebody speak about the future, or when someone uses today simple, present continuous or present ideal in their initial words: https://dictionary.cambridge.org/grammar/british-grammar/reported-speech-indirect-speech Source