Determine a supernet for the branch office. In the transit gateway route table, add an aggregate route that targets the VPN attachment. Replace the specific subnet routes in the transit gateway route table with the new supernet route.

Create an AWS Direct Connect gateway and a transit VIF. Associate the Direct Connect gateway with the transit gateway. Create a propagation for the Direct Connect attachment to the transit gateway route table.

Create a dynamically routed VPN connection on the transit gateway. Connect the dynamically routed VPN connection to the branch office. Create a propagation for the VPN attachment to the transit gateway route table. Remove the existing static VPN connection.

Create a prefix list that contains the new subnets and the old subnets for the branch office. Remove the specific subnet routes in the transit gateway route table. Create a prefix list reference in the transit gateway route table.