You can add and manage members of an approval chain in the corresponding approval chain management screen of the Administrator Tools.
Display the Administrator Tools menu
Click the Approval Chains button.
Find the row for the approval chain whose members you want to manage.
Click the Manage Members button.
The members row of the approval chain opens.
To add a member, click the Add Approver button
All users in your account are listed with three buttons beside the user's name:
Add as Required, In-Sequence
Add as Required, Not In-Sequence
Add as Optional
Clicking one of the buttons adds the user to the corresponding approver group.
Click the button for the approval chain group to which you want to add the user.
The user is added to the group immediately.
If the person is not a member of any of your organization's boards…
Choose Add a new member.
Enter the information for the board member and click the Add Member button.