@using Umbraco.Cms.Core
@using Umbraco.Cms.Core.Services
@inject IContentService ContentService
@{
// Create a variable for the GUID of the page you want to update
var guid = Guid.Parse("32e60db4-1283-4caa-9645-f2153f9888ef");
// Get the page using the GUID you've defined
var content = ContentService.GetById(guid); // ID of your page
// Get the page you want to assign to the document picker
var page = Umbraco.Content("665d7368-e43e-4a83-b1d4-43853860dc45");
// Create an Udi of the page
var udi = Udi.Create(Constants.UdiEntityType.Document, page.Key);
// Set the value of the property with alias 'featurePicker'.
content.SetValue("featurePicker", udi.ToString());
// Save the change
ContentService.Save(content);
}