That looks like it could be damage from cold.......or sitting in plastic bag with the leaves pressed against the outside (and probably also too cool) or the plant was grown in ideal conditions in a greenhouse and than brought into "normal" conditions causing damage to the leaf. In any case that is not from under or overwatering. With proper care it should grow out fine but I would also probably removed the larger damaged sections.

Or tender leaves cooked in a hot sunny window since cold isn't your problem?

FataMorgana

nope FataMorgana my area is hot..... 37degree C during daytime

yes. That was what I was meaning. Sitting next to a sunny window on nearly a 100 degree F day could cook tender plants.

FataMorgana

FataMorgana what to do then .... i brought it back in my bedroom ..... hoping its condition will get better being in the A/C ,.... but how do i arrange sunlight for the plant then?