You would use Reach Effectors.

See this section in the manual: https://manual.reallusion.com/iClone_7/ENU/Content/iClone_7/Pro_7.4/08_Animation/Reach_Target/Creating_Body_Motions_with_Effector.htm?Highlight=reach%20effector.

The character uses an ax, but the same would apply to a spade.

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I have created a character whom I would like to have digging. I have iMotion_Career Motions plus I have a prop of a spade.

My problems start when I try to attach the spade to my character. 

How to I attach the spade to both hands on my character or do I need to use a specially designed prop. The one I am currently trying to use is from a tool download from iClone store. I can attach the spade to the right hand of my character but don't know how to attach it to the left hand. I have looked on youtube and have found a demonstration but the prop is automatically attached to the right hand when it is added to the project thereby making attaching it to the left hand appear easier.I imagine I have to use at least one dummy box.

I would be very grateful if someone could help me out on this.