question

You can refer to the following Cloud Script sample to write a function that invokes the server API GrantCharacterToUser. You can find many samples in the title’s default Cloud Script revision. For more detailed information about Cloud Script, please check the doc -- CloudScript. Besides, you can check this doc -- How to modify read-only or internal player data from CloudScript to learn how to execute the Cloud Script function via Client API ExecuteCloudScript.

handlers.grantCharacterToMe = function (args, context) {
    var request = {
        PlayFabId: currentPlayerId,
        CharacterName: "FighterDude",
        CharacterType: "Blue Warrior"
    };
    // The pre-defined "server" object has functions corresponding to each PlayFab server API 
    // (https://api.playfab.com/Documentation/Server). It is automatically 
    // authenticated as your title and handles all communication with 
    // the PlayFab API, so you don't have to write extra code to issue HTTP requests. 
    return server.GrantCharacterToUser(request);
};