You are referring to the trade in trepang (sea cucumbers) conducted by Makassan fishermen along the coast of northern Australia, mostly between roughly 1740 and 1900. Trepang was a delicacy in fashion for Chinese cookery after 1600, so the ultimate destination of the catch was China. But there is little to no evidence that the Chinese themselves visited Australia.

I discussed the Makassan trade with Australia in more detail in an essay here. You might also be interested in Joseph Needham's discussion of the discovery of a statue of the Chinese sage Shao Lau, which was supposedly found embedded in the roots of a 200-year-old banyan tree outside Darwin in 1879. This is often cited as evidence for explicitly Chinese contact with Australia's "Top End", but without any historical context (or indeed a reliable contemporary account of how the statue was discovered) it is impossible to say whether the story is accurate or a hoax, and, if accurate, whether the statue might not have reached Australia after passing through many hands, rather than directly on a Chinese boat.