Amply doesn't currently offer a certified manual D duct design capability. However, we recommend that our users who need that use a platform like Wrightsoft and QuickModel.
Wrightsoft
In Wrightsoft, there is a BTU or load override option, which allows you to directly enter in the loads that have already been calculated by Amply.
There is no need to redo the load calculation to complete a Manual D.
Draw simplistic boxed representations of the rooms in the building (or import a Amply floor plan to sketch on top of it). The rooms do not need to be dimensionally accurate, as they are simply a place to hold the calculations that have been already completed.
Use the BTU or load override option for each room and just directly enter the load calculations from Amply.
Continue with the typical Wrightsoft process for completing a duct design.
Kwik Model 3D
You can export a screenshot of an Amply floor plan and import that into Kwik Model to then complete your duct design design.