If the car insurance was cancelled due to non payment of the car insurance then you usually have up to 30 days to reinstate the car insurance policy.
After 30 days then the car insurance company may be unwilling to reinstate the car insurance policy but sometimes they will if you've been good at the other car insurance payments.
If you've been constantly late with payment then the auto insurance policy might not be reinstated and you'd have to search for a new auto insurance company.
If the auto insurance was cancelled for other reasons then they also might not reinstate the auto insurance policy at all and you'd have to signup for a new auto insurance policy through another auto insurance company.