What should I do if I apply for a US tourist visa but don't know the hotel information?

You can ask the travel agency to give you some information such as the address and telephone number of the reference hotel, and just find any hotel information to submit.

Generally speaking, this information will not affect your visa matters.

If you are really asked by the visa officer, you can tell the visa officer directly: you are in a tour group of a travel agency and you haven't decided which hotel!