Hello @CoreanS ,
If you already have a CSV or other file with these 450+ contacts, I'd recommend the following steps:
Upload the 450+ you want removed, and make a new list as part of the upload process. Call it something obvious like "700 for Removal."
Once uploaded, go to that list and select-all the 450 or so contacts in it.
With all the contacts in the Removal list selected, click Actions > Delete > select the list you want them removed from.
If you know a common element to segment out these 450+ contacts, you can use the segmentation tool. Then add the segment to a list, select-all, and delete.
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