How to add custom plugin to the cpack package

i have wrote one custom plugin , and i want the PACKAGE project can package the plugin
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i try to write the cmake in cmake_install.cmake like this
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it does true to package the custom plugin into the slicer project tree and running without error,but it can’t package into a exe file with the error below
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i guess i wrote a wrong way , it should not wirte into the cmake_install.cmake file,but i don’t known which file should do the work.