Admission and advisor selection
It sounds like you've been admitted to a US PhD program in computer science without guaranteed funding.
While you will have to decide for yourself what to do, to me this seems like an unusual circumstance. As Buffy's answer mentions, it's common for students to not have an advisor right away in US PhD programs. However, it is not common to be completely unfunded.
I don't know what led you to being in this position, maybe there was a miscommunication between you and the program you applied to. Did they think you would have some sort of funding from your home country? Did they think an advisor had already committed to taking you on (in my grad program this would have been referred to as a 'direct admit' student)? Did you not have any conversations about funding during the application process?
I would not recommend moving to another country for an unfunded PhD unless you are independently wealthy and the cost is no concern. If you can arrange for a TA or RA position before the semester starts then that's fine. It seems like you're out of luck for now on the RA front, so find out from your program what the steps are to get a TAship.