Help with pairing the right headset to a new 3T fork
Measure the inner diameter of the headtube, both upper and lower. These are the key measures in combination with the fork dimensions. You probably want to confirm that the angle of the inner chamfer angles are 45 degrees (and not 36) as well.

Once you have those measurements you can start searching. Note that it says "integrated" (= IS) on the Aventon page, which is also a key. It seems to me that there is a risk that you can not fit a tapered fork straightforwardly into your steering tube though, but Cane Creek can probably help you out there. However, that depends entirely on the measures you obtain.