OPTION 1
If the bolt in question was implemented from another software, for example Inventor,
you can save the bolt as an AutoCAD dwg format.
Open Inventor and save the element with a .dwg format to your desktop.
Open Advance Steel navigate to where you saved the file and open it. Make the
special parts is at (1:1) scale on layer 0 as a 3D Solid and the color is ByLayer.
This ensures that the special part will be inserted on the Special parts layer.
Save the file in the correct location
For example, if you are using the USA install the location will be as follows;
C:\ProgramData\Autodesk\Advance Steel 2021\USA\Shared\Support\Symbols folder.
OPTION 2
Additionally, if the bolt exists and you want to detail them separately, you can explode the bolt to solids.
Remember to save it in the correct location and import it as a special part.
Your INTERNAL and EXTERNAL BOMs should be modified to accommodate Special parts.