Dither can be applied from the Render Assistant (File > Render). The following steps are still valid and necessary when burning a CD to disc (for now).
When the time comes to truncate your audio to 16 bit, it is best to apply dither. In Triumph, you should save this step for your final render/burn - ideally, when you are ready to downsample. Don't worry though, dither will only be applied and truncation will only occur after sample rate conversion occurs, assuming you use the MBIT+ dither effect. To apply dither, you should do the following:
1) Drag either the Goodhertz Dither or MBIT+ effect from the Effects List (located under Goodhertz and iZotope, respectively) to the Master Layer. If you have additional effects on the Master Layer you should place the MBIT+ effect last or Flatten your workspace first. Note that Flatten will convert the sample rate to that of the output device, if the affected content contains multiple sample rates.
2) Select your dither options, by clicking the disclosure triangle to the right of the effect.
3) Select File > Render (or use the desired Render Action in the Actions List).
4) Select your desired bit-depth in the first Render pane.
5) Choose the rest of your render options and click 'Render.'
Triumph will then convert the sample rate to the rate you have selected, do any processing on the Master Layer and apply the dither noise. Lastly, Triumph will truncate the bit-depth and write your audio file/DDP/CD.
If your imported audio is already 16 bit and you have done no processing whatsoever, you can generally ignore this step. There is no need to apply dither twice.