Don’t worry, influencers understand they won’t be selected for every opportunity.
If an influencer applies for your collaboration and you don't wish to work with them, you have two options:
Do nothing and the influencer will be archived and notified after your deadline expires.
If you prefer to keep your list clear of unwanted applicants, you could click on the 'X' above their profile pic to archive them (cannot be undone). Influencers will be notified of this, but they will be grateful to be kept updated like this either way.