Typically, the plugin would be under that first file path and under the name 'com.axomic.openassetforindesign.extension' or something very similar. After you delete that folder, Apple uninstall instructions also recommend removing it from your 'Trash' folder, as well.
You can make sure that the plugin is uninstalled by opening up InDesign, clicking 'Window' > 'Extensions', and 'OpenAsset' should no longer be an option there. If OpenAsset was your only plugin, you might not even see the 'Extensions' option, which also means that the plugin was successfully uninstalled.
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