you can add them manually ini the band maths as described here (outdated description, but some steps are still valid): How to prepare Sentinel-1 images stack for PSI/SBAS in SNAP - #252 by bayzidul
you can add them manually ini the band maths as described here (outdated description, but some steps are still valid): How to prepare Sentinel-1 images stack for PSI/SBAS in SNAP - #252 by bayzidul