One of seed leave is turned yellow

Sterilize some scissors and snip that leaf tight to remove as much of the discolored portion, to stop spread of any rot or pathogens. You aren't losing much; it's just a cotyledon and with actual leaves showing, it's job was nearly done. Probably this resulted from the seed shell getting stuck, with water trapped, leading to rot. Alternatively a pest did some munching. If you see this happen consider using clean tools to pry the shell off; do not force and try again a couple days later if needed. Until it falls, keep seedling dry above surface until it comes off (harder outdoors of course) If possible I would keep seedlings indoors/protected a couple weeks longer at least; at this size they have zero defenses and are prey to earwigs and a million other little critters. Good luck!

Hi there! Sometimes the cotyledons get a bit tangled coming out of the seed, or otherwise get damaged early. Since the rest of the leaves, especially the first pair of true leaves, seem healthy you are probably good to go! Just keep protecting that fragile baby and make sure humidity is high and you should be good to go! Happy growing! 🌱👍

Might have been injured/damaged when coming out of its shell no fault of your own. I would not worry to much about it. looking healthy otherwise, but keep an eye on it. I'd recommend mulch around the base of the plant to prevent soil from splashing up on the leaves when you water. Dried grass can also work. Best of luck