Got it!
-
sudo runuser -u _gvm -- gvmd --get-users --verbose
(notice this should be two - characters between _gvm and gvmd, not a long dash). This should return the users (mine gave only admin), and their uid -
sudo runuser -u _gvm -- gvmd --modify-setting 78eceaec-3385-11ea-b237-28d24461215b --value <uid>
Where<uid>
is the long guid string you just got from the command above, for the user you are running openvas under)