The on-premises end of your L2VPN must be an NSX Edge appliance. You must configure this appliance and related on-premises vSphere networking before you can create an L2VPN.
If you have a compatible version of NSX installed in your on-premises data center, you can use your existing NSX Edge appliance as the on-premises (client) side of an L2VPN that connects to your SDDC. If necessary, you can download and deploy a standalone NSX Edge to use as the L2VPN client.
The "NSX L2 VPN Client" table in Understanding Layer 2 VPN lists compatible SDDC and on-premises versions of the NSX L2VPN software. To determine the version of NSX running in your SDDC, see Correlating VMware Cloud on AWS with Component Releases in the VMware Cloud on AWS Operations Guide.