Select the assignment for which you want to enable or disable the eBook from your Section Home. Click policies (A) and then select view & edit policies (B).

Click expand advanced settings (A) and then click edit (B) next to Resources.

Under assistance types is eBook and resources Check this box (A) to enable or uncheck it to disable the eBook. Click apply to this assignment only (B) so it does not alter your default settings. If you want to set this policy for all assignments, click save as default settings. Then continue to review & assign the assignment.