I have a low voltage transformer for my toro sprinkler system. It has a white, red and blak wire. It was broken and I was given a Hunter transformer with two yellow wires and one green wire. I was told this would work . How do I wire.

The person who said it would work, should have told you.
If this uses 24 volts and the transformer output is 24 volts and has enough VA(volt/amps), and
If I was to guess, red and black would be used for 240 volts and the white is capped, and for 120 volts, it may use the red and black for primary, and the red is capped.
If I was to try, I would hook up as mentioned above.
Have a meter hooked to the secondary and watch as you momentarily apply primary voltage, if it is close or likely a little higher with no load, it may work providing The VA's are there.