How to make sweet potatoes disintegrate in stew
This depends a bit on the kind of result you are aiming for, generally speaking most people struggle to keep their sweet potatoes "in shape" and prevent disintegrating:


For a slightly textured result, cooking your peeled and cubed sweet potatoes long enough should suffice, just make sure you have enough liquid in your dish and stir every now and then to help them break them up a bit.
If you want smoother results, stir vigurously or use a potato masher and "stab" your stew a bit once everything is very soft - stop when you reach the desired "chunkyness"/"smoothness".
But for a totally creamy and homogenous sauce you will need a food mill, a food processor or - even simpler - an imersion blender.