This is a SPO Admin (super-user only) function.
Open your own Action List. Enter the user's OtterID into this field and click the button to the right [help desk action list login]. The following example is for Marylou Shockley (shoc3141) Chair of Business AND Dean Kamath's delegate/alternate/back-up.
She currently has nothing to sign off as Chair. If they're a delegate like Marylou, use the drop-down menu they have to view the SO's Action List.
In her delegate roll to Dean Kamath she can get access to a proposal he needs to approve. We can only view the Action List. Marylou's and Shayam's have the live link to approve it (in the Id column).