restore original photo to iphone after switching to opimization mode

I tried the optimize iphone storage settings but when I wanna send photos to my friends using viber or other app chat, it did not appear any photos for me to send. Therefore, I decide to switch it back to the original mode. However, the problem is it just downloaded half of my photos to original resolution and it stopped. I still have 1 gb storage. Anyone could tell me how could I download all of my photos back to the original resolution?