You will buy the rubber strip seperate from the chrome trim. There are about 5 clips on the chrome that will grab the rubber as you put the new rubber onto the chrome strip. Those same clips will slip over the top lip of the door. Use that same piece of wood used in removal to gently hammer the chrome strip back into place. Trust me, you can do it. It will all fall into place after you remove the chrome.

Good luck,
Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S