Access Ec2 instance

Where are you trying to access it from? If you are trying to access from your corporate network, you need to create either an IPSec VPN connection or a DirectConnect connection to your AWS VPC. Then you will be able to connect to the EC2 machine, provided you have configured your networking correctly.

If you don't already have a DirectConnect, it may take some time to set-up.

You can set up VPN. Take a look at this - https://docs.aws.amazon.com/vpc/latest/userguide/vpn-connections.html

It depends there is multiple solutions

1. direct connect/ VPN (site-to-site/client).
2. bastion host.
3. connect through SSM session manager