You may want to download leads you previously uploaded to a campaign for multiple reasons - perhaps you want to re-target leads who didn't open any emails in your sequence (psst - you should do that if you aren't already!)
Now that we've talked about the 'why', let's talk about the 'how':
Apply a filter (optional)
Once on the 'Leads' tab of a campaign, simply use the 'All statuses' button to apply a condition that you need
Select individual or all leads.
Download selected leads.