The US president was probably referring to media reports that Iran could receive access to $300 billion for reconstruction as part of the memorandum of understanding with the US. In particular, the Financial Times reported that the Trump administration has proposed that the $300 billion fund for Iran be financed through private companies that want to invest in the country, rather than through governments.
Citing a source, the Financial Times wrote that Iran’s access to the fund will depend on its adherence to the new agreement. The fund is to assist the country's reconstruction and modernization efforts. Officials noted that there is interest from businesses in Europe, Asia, including Japan and South Korea, as well as the United States.