There are two ways of adding a Group to an eForm:
1. Drag and Drop
2. Using the eForm Menu
Drag and Drop
1. Drag the group and drop it to the eForm.
If you haven't tried yet, here are the steps on how to drag and drop a group to an eForm.
a. Hover your mouse over to the Group you're going to drag
b. Press down the left click button of the mouse. Holding the left click button down will allow you to move the Group.
c. Move your mouse towards the desired eForm and release the left click button of the mouse
2. Click OK on the confirmation window.
3. You can check if a Group was successfully added to an eForm by clicking anywhere (except for the two icons) on an eForm
Using the eForm Menu
Please refer to the article How does an Administrator add multiple profiles in a Group or an eForm using the "Bulk Add Members" and look under eForms.