I have used the collocation tool. The master product is a 10 bands S2 image and the slave product a vv or a vh band from S1 corrected.
But when I open the resulting product on qgis I see that the value of the S1 band is 1.0 everywhere on the picture.
could it be that you are looking at the collocation flag - 1 means that the pixel was covered by both products.
There should be the other bands as well. Please have a look at this tutorial: