RESET -- Restores run-time parameters for session to default values
RESET variable
RESET restores variables to their default values. Refer to SET for details on allowed values and defaults. RESET is an alternate form for SET variable = DEFAULT.
See also SET and SHOW to manipulate variable values.
Set DateStyle to its default value:
RESET DateStyle;
Set Geqo to its default value:
RESET GEQO;