Hello Lina Rojas,
To model module D, you need to consider only the avoided impacts. The input required to avoid those impacts are located in module C3 or C4, not in D.
To model avoided impacts you need to know how much heat, and how much electricity is generated from incinerating 1 kg of each of the three materials. If you use the EcoInvent dataset, this is usually described in the process description.
When you have the factors for each material, you multiply with the amount of each material.
This should give you an output of electricity, and an output of heat for each material. Then sum across heat, and across electricity. This should give you a total amount of displaced electricity, and displaced heat.
Select representative processes for which energy is replaced (In Denmark i use natural gas for heat, and residual electricity for electricity, but this depends on your geography).
Input the total displaced heat energy in the heat process, and select avoided impact. Do the same for electricity.
Calculate the product system, and this should give you negative impacts for the two processes.
Good luck