I don’t really understand the problem, sorry. Maybe you can first describe how you prepared your data until the step of interferogram formation.
Did you see that there is a python script which does this job for you? Snap2stamps package: a free tool to automate the SNAP-StaMPS Workflow
Also well documented here: https://gitlab.com/Rexthor/gis-blog/-/blob/master/StaMPS/2-3_snap2stamps.md