First install the pimoroni requirements on the pi:
git clone https://github.com/pimoroni/enviroplus-python
cd enviroplus-python
sudo ./install.sh
reboot
sudo reboot
Then setup the prometheus exporter by:
git clone https://github.com/KristianMischke/enviroplus_exporter
cd enviroplus_exporter
sudo ./setup.sh
Install the corresponding dashboard https://grafana.com/grafana/dashboards/18987-enviropi-prometheus/ or enter ID 18987