For several years I tried this and that to "delete" my chest wrinkles after sleeping on my side and squeezing my chest to create vertical wrinkles that would sometimes stick around for not only hours, but create permanent creases (you side-sleepers know what I'm talking about).
I have two remedies that work:
One is to tri-fold and then roll up a large tee shirt (a men's shirt or XL works great). I secure it with a rubber band and then a silk ribbon. I stick it down the front of my shirt (between breasts) and "hug" it while I sleep. This does really work!
The other is the Beautiful Chest Decollete Pad. I order these in doubles and keep them around. They work very well to not only help you not get the wrinkles in the first place, but also "iron" out creases that exist. The only caveat is that they wear out (lose the sticky backing), but I find if I wash it in warm water and let it air-dry in the morning I can prolong the backing and therefore it's use.