For Debian 10 run the following:
Keep in mind that the owner of the key may distribute updates, packages and repositories that your system will trust (more information).
echo 'deb http://download.opensuse.org/repositories/security:/csirt-tooling:/test/Debian_10/ /' | sudo tee /etc/apt/sources.list.d/security:csirt-tooling:test.list
curl -fsSL https://download.opensuse.org/repositories/security:csirt-tooling:test/Debian_10/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/security_csirt-tooling_test.gpg > /dev/null
sudo apt update
sudo apt install intelmq