Hand feed a 2yr old cockatiel?

my cockatiel is a very unhealthy eater and only eats seeds, hes kind of skinny and is very averted to eating anything new..so i bought a small syringe to try and do some hand feeding and get him a lil chubbier/healthier, what formula is good for older cockatiels? would u recommend doing it? any tips? simple recipes? im hoping to get some more professional opinions but any experienced opinion well be greatly appreciated. also please dont try and suggest those 1:4 new:old change of food brands or placing fruit in their cage and wait for them to eat it cuz i spent too much already on throwing away uneaten foods.lol