Q.You Mention In The Mango Fungicide Article That Trees Should Be Treated Before They Have Fungus – What Can I Do Now That It Does.
I live in kid north coast NSW. Two mangoes side by side exhibiting fungal issues, but also some dead branches in shady parts of Tree. Trees are sick and infected and very large – what can be done.

Certified GKH Gardening Expert
Unfortunately, your photos did not come through. I am unable to ID what infection is causing the damage.
Some are treatable, and some are not.
You can try broad spectrum fungicides, but you will get better results if you know what disease is causing the die-off.
Here are some articles to help you with general fungicide use:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm