Right, you're trying to gradually lower the temperature in there to match (or come closer to) outside temperatures. So remove or reduce one heat source, give it a 1-3 days, reduce more, etc. They can take it, but if it makes you feel safer, you can do a more gradual reduction.
Assuming you're talking about sectioning off part of the run, at night you'd bring them back into the unheated brooder still located in the shop, OR you move the brooder into the coop (which sounds like the more difficult thing). I integrate in the run first, moving into the coop is the last step.
Ok, so let's work on getting them off heat first. Integration will come after so that way you know they can stay out during days without issue.
:D Reason I asked is because I think it'd be simpler to just section off a corner of the run than to worry about moving the brooder around due to...
So for weaning them off heat, I'd kill two out of three heat sources right off the bat - if the shop stays heated no matter what, then you can probably turn off the heat lamp and that should encourage the chicks to use the plate if they should need it. If the shop doesn't need to be heated then...