Welcome to the forums.
I have moved your thread to the Emergency Room section of Talk Budgies where it's most appropriate.
I'm very sorry for the condition in which your budgie is currently in.
From that photo I can see a big inflammation on the eye and unfortunately it's very likely that basic care provided at home will not effectively solve the issue, as the case seems to be very advanced. Your budgie needs urgent professional medical attention and to be properly diagnosed and treated by a specialized avian vet.
If there is none in your area, you can have a regular vet consult with an avian vet and upon explaining the situation you can get the right medication to treat your budgie.
Have you quarantined this budgie from the rest of the flock? If not, then I suggest you separate this budgie, as a safety measure and in hopes of the disease to not spread in case it's contagious.