.On making use of Tangent Chain command you need to select only one edge and all other edges forming a tangential chain with your selection are automatically selected.
When the current selector of a command accepts the selection of curves inside solids (which you can check by opening the Selection Filter dialog box: if the Solids check box in the Inside area is selected, then the condition is verified), the Tangent Chain command will be contained in the context menu displayed by right clicking in the graphics area.
When you invoke the Tangent Chain command, the selection of free edges of an open solid is enabled and the cursor immediately changes to .
Select an edge of the loop that will act as the start edge.
All other edges that are tangentially linked with the edge you selected are automatically selected. The selected edges are highlighted by a red dashed line.
If you try to select an edge that does not belong to a loop, the selection will not be permitted and a proper warning (along with the signal 
) will be issued.