Unfortunately, it is not possible to objectively verify this claim because it is based on speculation.
The text post shared on Reddit and Facebook as early as 23 March 2020 says that China is the creator of the COVID-19 pandemic and predicts that due to the lack of trade of China-based European and American companies' shares would fall 40% of their value. The text post also says that China would buy 30% of the shares of falling companies from the United States and the UK and that it would own those companies in China.
This text post has been circulated on various social media and discussion forums with a caption that it might also be a conspiracy theory.
There have been several news reports of some American company shares falling by percentages in singular digits by the end of March 2020.
However, due to lack of evidence and credibility to the contents of the viral text-post, as of now, it is not possible to prove the veracity of this claim.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.