yellow start from bottom,can someone help ^^

Ok looks lovely! The two bottom leaves have finished all they can, they are the two very first leaves (cotyledons) you see on your sprout/seedling. And as the plant progresses you will lose more of the lower leaves that's fine. As for overall plant health, she looks fine. A few tiny blemishes/spots/marks are quite normal and nothing to worry about. Could be a slight nutrient deficiency but if so would be all over the plant pot in more than one or two tiny places. Could be wind damage/light damage. Could be some nutrients dribble feel on that leaf and just " burnt" onto it. Could be your first sign of pests(generally seen on the underside of that damaged leaf), they can be microscopic so you may not be able to see them without zooming in a photo or using a magnifying glass?