Go to your nearest computer sales/repair store, take the cooler fan assembly & remaining screw with you.
But i would be worried about if the missing ones are in the case (or psu) and may cause a short.
No, you should not continue using the pc in case the final screw gives way, the fan drops and damages other components?
My PC- Ryzen 5 5600x, B550 aorus pro ac, Hyper 212 black, 2 x 16gb F4-3600c16dgtzn kit, NM790 2TB, Nitro+RX6900XT, RM850, Win.10 Pro., LC27G55T.