Thanks a lot for your input, MCT358 :)
I spoke to Victor, the Sales person at 7L, he said it is not a big deal(the nails are for decoration purpose only) and eventually i have it solved by myself. Result is quite acceptable at least to me... Very simple to do, frankly, i put the steps here for anyone had this kind of problem (it is minor but still annoying), hope it helps:
1. i used a deformed u-clip to measure the depth of the hole, cut a tooth stick tip to match the measurement.
2. use u-clip tip carefully insert small amount of glue inside the hole.
3. insert tooth stick tip inside the hole, use a looney's edge gently press it in to flatten. then use dark shoe cream to color it in order to fade it out among the others.(i used my GF's nail oil :)
4. et voilà!