AWS: Using TLS-certificate without private key

For using an API from the dutch chamber of commerce, It's mandatory to install a TLS-certificate from the Dutch government. Only when the certificate is installed, It's possible to make authorized API-requests. The chamber of commerce has published an install guide here: https://developers.kvk.nl/support/documentation/manual-tls-certificate

We want to use this API in an application that's hosted with AWS amplify as backend with React as frontend. The most obvious approach was using AWS certificate manager, because it's integrated with Amplify. The problem we encounter using the certificate manager is that It's mandatory to provide a private key in PEM format to import a certificate (see picture). The thing is, there are no private keys given since the certificates are from the governments, and the manual does not describe what needs to be done in our case.(https://i.stack.imgur.com/uBXRl.png)

We tried to contact the chamber of commerce but our response was that it was not in their reach and we should try it elsewhere. Our only option as we see now is that we need to host a dedicated server to redirect the api requests and responses, but that would defeat our point of being serverless with Amplify.