[Resolved] How to connect translation

On a clients website (which I did not build) I had to recreate a page.
I did so by copying another page with similar content. That page I gave a slightly different url. Once finished I deleted the original page and changed the url of the correct page to the one I did delete.
My question: how can I link the 3 other already existing language versions to this 'new' page. At the moment only the German language switcher flag is visible. I do understand why, but would like to change this, just in case a visitor would like to switch languages on this page.