TinkerCAD Align to Odd Shaped Object
Consider to construct an object of any suitable shape that will properly align with the edge of "A."

The attached image is certainly an odd-shaped object (from a previous test project).



Add a regular/symmetrical object such as a cube and size it appropriately for your purpose. It would not have to be a cube, although such a shape provides for convenient alignment in this case:



Use the alignment tools feature in Tinkercad to align the desired edge(s). In this case, alignment is common right side, centered top to bottom.



After clicking on the alignment button, lower right corner:



Group the two objects using the Group feature.

I created a sample alignment reference in this image and placed it in contact with the group.



Move the group or reference item the desired distance:



Select the group and ungroup it.
Select the initial alignment item and delete it.



Objective completed.