Yes, it is possible to convert a private subnet to a public subnet after creation. To do this you will need to make the following changes:
- Confirm there is already an IGW (Internet Gateway) attached to the VPC. This should be the case since you already have the public subnet.
- Update the route table applied to the subnet (AWS Management Console -> VPC -> Route Tables) to include a route to 0.0.0.0/0 -> IGW.
- Assign public IP addresses to your resources.