The easiest way to do that is to upload that list of emails with just the email address (one single column in your csv file).
The you do the upload, apply whatever tag you want. That will tag all of those emails addresses with that tag. It will also create duplicate contacts.
Then, go into Admin - Data Cleanup and run the deduplication process.
After the duplicates are determined, run the ‘automatically merge duplicates - add content, don’t overwrite’
That will merge your email/tag with the existing contact record and the existing contact records will now be tagged with the tag you want
Hope that helps.
4Spot Marketing • https://4SpotMarketing.com
Infusionsoft/Keap Certified Partner, StoryBrand Certified Guide
PlusThis Certified Partner, Zapier Certified Expert, Integromat Expert
11700 W Charleston #170-160 • Las Vegas • NV • 89135
O: 702-721-9763 • C: 702-525-9763