You can use the `PORTAINER_LICENSE_KEY` environment variable.
For example:
docker run -d -p 8000:8000 -p 9443:9443 --name portainer --restart=always -e "PORTAINER_LICENSE_KEY="<license key here>" -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer-ee:latest