The cause of the oliguria needs to be clarified.
Pre-renal requires treatment for the cause.
Correction of shock, blood volume replacement, treatment of heart failure, etc.
Renal would require management according to its primary cause.
Post-renal requires a urological consultation for indications for surgery and early surgical treatment if surgery is not contraindicated.
If non-renal, diuretics can be given with blood volume replacement, those with hyperkalemia need prompt management, and those for whom general treatment is ineffective should undergo dialysis.