i DON'T KNOW THE Prochem leather products............but I suggect you use the product to make foam, in a bucket...........use sponges, both, to create the foam and themn apply it.
BEWARE OF LOADING TOO MUCH ONTO THE SPONGE, as you must avoid the foam / water running down............it will leave streaks............to avoid this, soak the sponge squeeze it, 75% dry, then cover an area, an arm, or a side , or single cushion, quickly, immediately, run over the cleaned area with a towel, then go over the entire suite in this way.....
You may have to repeat this, to get a good result, possibly even repeat it twice.............but this is safe, provided that the chemical is not too strong and critically..........you don't rub too hard.
This is very basic info and you should get onto at least, a one day course with either of the two providers on here.
One is Harrogate based ( LTT ) the other is in Newcastle ( currently has a vacancy on a one day course ) Furniture Clinic.