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1). Since one does a scientific research of computational simulation, the preparing input file for the simulation by himself is one of the regular jobs for him.
2). The estimation of formation energy for your system is quite simple. The formation energy can be estimated in the following way:
step 1: perform the geometry optimization and the total energy calculation for the perfect GNR (i.e., no doping or adsorption of a biomolecule) and extract the value of the corresponding total energy.
step 2: perform the geometry optimization and the total energy calculation for isolated biomolecule and extract the value of the corresponding total energy.
step 3 perform the geometry optimization and the total energy calculation for the whole system of biomoelcule doped or adsorbed GNR and extract the value of the corresponding total energy.
step 4: formation energy = total energy obtained in step 3 - total energy obtained in step 2 - total energy obtained in step 1
Note: the size (i.e., length and width) of GNR in steps 1 and 3 should be same, and the k-point grid size are also same.