I'm not sure of the question. I think you'd remove the collar in the same way you'd remove the cake. (Is there parchment on the bottom, too?) If so, just carefully run a knife between the collar and the pan, and the collar and the cake. The collar should slip out, and then you can flip the cake out. If that doesn't work, you can trim the collar to the edge of the pan, and then flip it out and remove the collar. This is assuming there is parchment on the bottom as well. If there isn't, you may need to carefully slip a small spatula under the cake to loosen the bottom of the cake so it doesn't stick to the pan. I hope this answers your question. If not, please clarify.
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