Hi,
Had a similar situation about 2 years ago.
Go to any large pet store (if not, go to
Serangoon North Ave 1 bird shops around Blk 152) and they would have the following:
Kaytee Exact Hand-Feed Formula
The website for this product can be found
here.
Please follow the mixing instructions precisely as documented
here.
There is a video that shows you how to feed a baby bird properly, found
here.
Your biggest problem is NOT the food itself, but the investment of time & care (and $$$ as the above cost $20 per bag).
If you suspect the nestling is less then a week old, there is a 70% chance it will die no matter how well you handle it. Are you prepared for this?
If yes, you will have to be the caregiver for the next 2 weeks for at least 12 hours a day. Are you prepared for this?
If yes, PLEASE READ THIS VERY CAREFULLY. Nestlings require very special feeding techniques and you need to monitor it's crop (droppings) to ensure the food is getting into it's body correctly. The best way is to measure it's weight, but you need to get a gram scale to do so.
If you don't think you can commit, pls send it to SPCA to put it out of it's misery.
Otherwise, good luck and keep trying till it's about 2 weeks old.