yuṭ is the augment of dīṅ of an ārdhadhātuka affix beginning with a vowel and having an indicatory k or ṅ,
Thus उपदिदीये, उपदिदीयाते and उपदिदीयिरे ॥ The Personal ending is कित् by 1.2.5. दीङः being in the Ablative case, the augment is applied to the affix. This augment, however, is not to be considered as asiddha 6.4.22 for the purposes of semi-vowel substitution under 6.4.82. If that substitution were allowed, the augment would become useless. Why before an affix having क् or ङ् ? Observe उपदानम् ॥,