How to set client scope mappings via APIs?

I am trying to set clientScopeMappings using Keycloak APIs but I am not able how to define it after import entire realm first time. On first time, I call a POST on admin/realms sending a big json with the following attribute:

  "clientScopeMappings": {
    "realm-management": [
        "client": "myclient",
        "roles": [

This is running smooth to create new realms but how can I define clientScopeMappings when I am tyring just to add a new client to realm?

I have read docs for Keycloak 15.0 but I didn’t figure what API should be used.