The (sad) answer is that while such accounts have existed, none has been found by historians so far (but the search is not over). The recent book The Chinese and the Iron Road, edited by Gordon H. Chang (2019) addresses this issue in several of its chapters. One of the authors, Barbara Voss, writes:

To date, no personal writings, letters, or diaries of Chinese railroad workers on the first transcontinental railroad have been found. With notable exceptions, the Central Pacific Railroad did not even record the names of most individual Chinese workers, instead “working and paying them by the wholesale.” Although newspaper journalists wrote extensively about Chinese railroad workers, the journalists generally interviewed white supervisors, not the Chinese workers themselves.

As noted in the introduction of the book, the usual explanation for this is that workers were illiterate. However, there are contemporary testimonies that claim that many workers not only had at least a basic level of literacy, but that they wrote letters to China. In 1869, the New York Evening Post stated that

[t]he large number of Chinamen now in the Pacific states who all, or very nearly all, can read and write, have sent to China, in private letters, a vast amount of information concerning those states and the United States generally.

It is thus likely that many workers wrote about their experience to their relatives and kept records. However, the only type of document that has been found in Chinese archives are remittance letters used to send money back home, and they talk only about money. About the lack of private letters, Chang et al. write in the introduction:

The home areas of the workers in China suffered extensive devastation due to social conflict and war in the nineteenth and twentieth centuries, and every Chinese community in America in the mid- to late nineteenth century suffered arson, looting, and other forms of obliteration.

It is also believed that the houses in the workers' home villages, where such letters were kept, were poorly equipped to preserve paper documents (this changed only in the 1890s).

There is a wealth of folks songs, ballads, and poems that circulated in China about the life of its expatriate workers, gold miners or railroad workers. Some are positive and hopeful, and emphasize the success of the worker coming home flush with cash, while others are more sobering, such as this one:

In the second reign year of Haamfung (Xianfeng [c. 1832]),

a trip to Gold Mountain was made.

With a pillow on my shoulder, I began my perilous Journey:

Sailing a boat with bamboo poles across the seas,

Leaving behind wife and sisters in search of money,

No longer lingering with the woman in the bedroom,

No longer paying respect to parents at home.

Source

Chang, Gordon H., and Shelley Fisher Fishkin, eds. The Chinese and the Iron Road: Building the Transcontinental Railroad. 1st edition. Stanford, California: Stanford University Press, 2019.