in NGLClient goto
Administration -> Configure System ->Patron->search
Search the patronId which was put on hold.
Case 1)
Check the membership status.
If membership expired. Extend the membership expiry date then save.
or else
Case 2)
If the patron has crossed fine limit, then also the id will put on hold.
for that, collect all fine amount, then fallow the procedure.
1)search the patron then select that patron
2)click on Activate/Deactivate Live Patrons
then fallow the step by step procedure shown in below image.