Log in to the data service here, by choosing DLR ATMOS data service: https://acsaf.org/datarecord_access.html
or directly from this link: https://atmos.eoc.dlr.de/products/
Log in with your username and password.
After logging in to the data service, you should find the NO2 and H2O data records e.g. from GOME-2 on Metop-A from: "Index of /products/gome2a/level3". (And similarly for GOME-2 on Metop-B).