In order to exclude people/companies from a campaign,
There are 2 ways:
Use Sales Navigator (premium plan on LinkedIn) and use the filters in order to exclude the companies you do not with to be in your campaign.
Use external tool to scrape a LinkedIn Search.
Then export it to a CSV.
In the CSV, omit the lines you do not wish to be in the campaign.
import the CSV in the campaign settings.
Eh Voila, you are done....