How to use refresh token by using Keycloak Admin REST API

Question

I'm trying to use Keycloak Admin REST API SDK.

Then, I want to use refresh token to generate access token.
I know that the following code code can generate access token by refresh token.

val token = Keycloak.getInstance(serverUrl,
  realmName,
  userName,
  password,
  clientId,
  clientSecret)
  .tokenManager()
  .refreshToken()

But this code can only work on TokenManager.
I want to use any refresh token like following code by admin user.

// I hope to call token endpoint -> /realms/{realm}/protocol/openid-connect/token?grant_type=refresh_token...
val accessToken = tokenManager.refresh(String refreshToken);

Could any SDK Class refresh token as I want?