Access to the old UI has been removed as of today. 

GenerateAfter can help here.

///do ##class(Test.GenerateHelper).Generated()
///Hi there!
Class Test.GenerateHelper
{
  ClassMethod Generated() [ CodeMode = objectgenerator, GenerateAfter = Helper ]
  {
    set text = ..Helper()
    do %code.WriteLine(" write """ _ text _ """")
  }

  ClassMethod Helper() As %String
  {
    return "Hi there!"
  }
}