【Harmonize】 ,  【tune】 ,  【attune】  mean to bring things into accord with each other.

【Harmonize】 stresses as its end the combination of two or more things so that they go together without loss of individual identities yet constitute a frictionless or pleasing whole.

【Tune】  implies the adjustment of one thing to another or of several things to each other so that they will conform to each other or work in harmony with each other; thus, to  【tune】  a piano is to adjust its strings so that the tones produced will conform to a standard pitch or to a predetermined temperament; to  【tune】  up the instruments of an orchestra is to adjust the instruments so that they will produce harmonious tones; to  【tune】  up an engine is to make all the finer adjustments of its parts necessary to smooth operation. In literary use  【tune】 still implies adjustment (as of expression to a mood or of mood to a situation or need).

【Attune】  stresses the attainment of aesthetic harmony more than  【harmonize】  does, and it seldom suggests the idea of mechanical operation or effect often so strong in  【tune】 .