By means of ab initio calculations based on density-functional theory we demonstrate that magnetism in monoatomic Fe wires deposited on nanostructured Ir(100) surface can be tuned by their functionalization with hydrogen. The pristine monoatomic Fe wires deposited on nanostructured Ir(100) surface partially covered by H atoms are antiferromagnetic. However, the type of exchange interaction between Fe atoms can be changed by increasing H coverage. At fully hydrogenated Ir surface the Fe wires themselves are decorated with hydrogen, which gives rise to the ferromagnetic coupling between adjacent Fe atoms.