I am new to the Softstep and have just been programming it to control similar things in my Ableton set. Are you using the Advanced editor? Softstep 1 or 2.
In the advanced editor, you will need to experiment with a modline: Foot ON > either LINEAR or TOGGLE and outputting either a midi note OR CC > one of those combinations should work. This also depends on how thingS are set up inside your Ableton set - sometimes toggling a midi note didnt work for me, with an on+off switch in an effect in Ableton but was fine opening up an aux send. I have some mute on+offs in a utility plugin for some effects and I had to invert the values inside Abletons midi browser to make those function correctly, so its >>>TRIAL AND ERROR, I AM AFRAID. It took me a whole day to program simple stuff like that because of having to go back and forth between the editor and Ableton. But i got there in the end.
I am using Softstep 2 in standalone mode. I saw in the manual that in Softstep 1, standalone mode does not retain preset or scene inital settings - so if you are using SS1 you might have to be in hosted mode.