Had to look for some proper advice here too.
If the blackbird chick is kinda weak you could try to dissolve some glucose or dextrose in some water and try feeding it with a pipette perhaps. NO milk.
Read about cat's food (out of little tin) worked too. Also to boil an egg hard, made smaller with fork, with a dry bisquit (and a tadski water) through it. Quite small amounts per time. Worms, if you can find them/made shorter/smaller, are fine too. Spiders (which I thought is a no-no for you), flies, musquitos, snails (made smaller), etc.. are okay also.
Thing is.. you have to feed it.. very young bird don't have a 'get food' need, intrinsically, I believe. Stupidly they will not initiate searching for food themselves.
Well, good luck with it, Bodie.. hope you'll succeed.