In the given reaction, Cu(I) of Cu2Os) and Cu2S(s) shows reduction and form Cu(s)while sulphide of Cu2S(s) shows oxidation and form SO2(g) as shown below.
Therefore, Cu (I) of Cu2O(s) and Cu2S(s) acts as oxidant(oxidizing agent) and sulphide of Cu2S(s) acts as reductant(reducing agent)