Can someone tell me the preprocessing steps for Entropy-alpha decomposition of sentinel-1 dual pol SLC data?

it is possible, but the outputs are not very good. I tried to explain it here: H-Alpha Plane Problems - #34 by ABraun
In the named example, HH/VV is used and the data was simply not suitable to represent all scattering mechanisms. So VV/VH has even less information because it lacks horizontally transmitted signals.