Rear Door Glass replacement

OK be gentle with me as I realise this is pretty noddy.
I a have the new glass for the rear door of my defender 90. The instructions are so helpful - remove the window and seal carefully as you need to use the seal to fit the new glass.
Now I pride myself in not be totally stupid ( not far off granted ) but the lack of clarity is causing me to pause and ask advice. Nothing wrong with the seal today and want to avoid buying a new seal if I can.

Before I start - anyone got any tips or advice on this?

hi there.
do you have any strong cord or something like
feed cord into rear or rubber seal inside back door tighten carefully ease window out starting at one corner works for me

Thanks Dave - sorry for the delay, not a lot of internet connectivity during the last week, I like the idea I will have a go at it today.