There are 2 cidr blocks in a single AWS VPC. The cidr block A is connected to an on-prem network via direct connect but the cidr block B is not.

How do I reach a server X on the on-prem network from cidr block B? Can this be done with routing such as specifying the cidr block A as the next hop or should I provision a Load Balancer in cidr block A to forward traffic to on-prem?