The cubic noncentrosymmetric structure of the B20 compounds produces the spin helix with the wave vector balanced by the competition of two interactions: the large ferromagnetic exchange interaction and small antisymmetric Dzyaloshinskii–Moriya (DM) interaction . The mixed FeCoSi compounds demonstrate a switch of the sign of magnetic chirality in dependence of concentration . The sign of magnetic chirality is dictated by the structural chirality and chemical elements (Fe, Co) as well. The switch of chirality is accompanied by transformation of the helix structure to the ferromagnet and is observed at . Moreover, this transformation (helimagnet–ferromagnet) occurs as a function of temperature. We observe the decrease of the helical wave vector with lowering temperature from K and its abrupt zeroing at K. The magnetic field applied not along the easy but along the hard anisotropic axis is able to restore the helical structure in the temperature range below . The mechanism of the transformation is theoretically described by a competition between the cubic anisotropy and the DM interaction. We show that anisotropy-induced ferromagnet has nonreciprocal magnon spectrum due to DM interaction even in the absence of external magnetic field.