In order to microdose oral DMT, you'll first need to fully inhibit gut MAO-A using Moclobemide (preferably, especially if using it during the day and wanting to still be active and such), or Harmalas/Rue/Caapi, but i would say either Moclobemide (if you can get it), or Rue seed or Rue/Harmala extract (maybe pure Harmine or Harmine/Harmaline mix).
In terms of DMT dosage, idk, and the dosage of DMT depends on the dosage of the MAO-A inhibition since more MAO-A inhibition requires less DMT and less MAO-A inhibition requires more DMT.
They say you can microdose DMT by smoking some, maybe Changa would be an alright way to go, or doing a tiny little bump nasally perhaps.
Another thing one could do is track down some mushrooms or 4-ACO-DMT and microdose that, can even mix it with a low, moderate or high dosage of the MAO-A inhibition for synergy and a little potentiation and possible elongation of duration of the microdose.
But if you're willing to inhibit gut MAO-A, microdosing DMT is possible. Otherwise, you can try microdosing just the MAO-A inhibition and see if that helps you out any.