Shiny application inside template of another app

Hi,
I have been working in some shiny app but recently my client want to change the user interface.
I started to implement a new template with my code:

ui = shiny::htmlTemplate(
  # Index Page
  "www/index.html"
)

and now I am trying to embed my old application in one of sections inside index.html. I have not succeed so far. Is there any way around without recreating everything from beginning?

Thx