When you want to remove suppressed contacts from your campaign, please follow these steps:
go to campaigns > open a campaign
click prospects on the top right corner
go to more filters > suppression > yes
list of suppressed contacts will appear
select all contacts > remove from campaign
This is how you remove the suppressed contacts from your campaign. You can also check out these articles for further information:
How can I permanently suppress any outreach to prospects and companies?
How to remove companies/prospects from the suppression list?
What does 'suppress contacts' do?