Assuming you mean the AOD, try Settings>Display (make sure Night Clock isn't on during hours that you want to view the AOD)>Always On Display>(on this screen, take a second to make sure that "Show always" is selected) Layouts> then scroll to the bottom (on my S7E, at least) and select the screen layout on the bottom left. You can enter text in a field there.
You may have changed the AOD layout, or set Night Clock to hours that over-ride the AOD.