My car is making a rattling noise in the valves. How do I fix this?

Stop driving it if you haven't already done permanent damage , and get the low oil pressure problem diagnosed. That may answer your question of how to fix it.

ck oil level asap.

The rattling noise is your valves and you need to replace them and after you do that you need to get an oil change because if you don't you'll have the same problem again after maybe a week of driving your car, stop driving your car immediatly and get the problem fixed or you'll just blow your entire engine(NOT GOOD!!!)