You mention the Death record of Christopher Benson but your screenshot is of a Source Citation against the Death record of Nicholas Boyes.
So nothing you do to the Christopher Benson record will have any impact on this Source Citation.
If you widen the 1st column by dragging the header divider you will see:
T = Title
T = Type
A = Actual Text
which are the fields in the ‘GRO’ Source record that would appear to have been cited by mistake.
To remove that mistaken Citation click the red X Delete Citation button below.
However, that will not delete the ‘GRO’ Source record.
BTW: GRO is an unusual Title for a Source record with specific details for the Death of Christopher Benson.
Please explain the background to this Source record.