how can we get big fruits
I have 3 acres of guava trees but no big fruits. Most of them are only about lime size. The kind I have is Chinese dragon.
There are an awful lot of different plants that are called "guava." It may well be that this is the natural size of your variety; Wikipedia says guavas are usually from 1.6 - 4.7" I can't find any information on "chinee dragon," but if you can get information from the source you purchased from, that might be useful. This article might also be useful: https://www.gardeningknowhow.com/edible/fruits/guava/growing-guava-fruit-trees.htm
Also, the county extension service could be a good source of information. This link will help you locate the nearest one: https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm