using LukeHagar.PlexAPI.SDK;
using LukeHagar.PlexAPI.SDK.Models.Components;

var sdk = new PlexAPI(accessToken: "<YOUR_API_KEY_HERE>");

var res = await sdk.Playlists.UpdatePlaylistAsync(
    playlistID: 3915D,
    title: "<value>",
    summary: "<value>"
);

// handle response

This response does not have an example.