The effect of the molecular chirality of chiral additives on nanostructure of the twist-bend nematic (NTB) liquid crystal phase with ambidextrous chirality and nanoscale pitch due to spontaneous symmetry breaking is studied. It is found that the ambidextrous nanoscale pitch of the NTB phase is increasing by 50% due to 3% chiral additive, and the chiral transfer among the biphenyl groups disappears in the NTB* phase. Most significantly, a twist-grain boundary (TGB) type phase is found at c>1.5wt% chiral additive concentrations below the usual N* phase and above the non-CD active NTB* phase. In such a TGB type phase adjacent blocks of pseudo-layers of the nanoscale pitch rotate across grain boundaries.