Hi Jaden,
This might not be possible.
https://learn.microsoft.com/en-us/azure/vpn-gateway/azure-vpn-client-optional-configurations#routing
If you still wanted to try it:
https://learn.microsoft.com/en-us/azure/vpn-gateway/azure-vpn-client-optional-configurations#routing to get traffic to show up in your VNET (if it doesn't get dropped).
You can attach a route table to the GatewaySubnet to define the next hop which could be an Azure Firewall, NVA, or NAT Gateway (https://learn.microsoft.com/en-us/azure/nat-gateway/tutorial-hub-spoke-route-nat?tabs=portal#create-hub-network-route-table).