To get OV5640 working for your Allwinner H3 based board:
Step 1. Update the fex file
The file is usually located in /boot directory, name could be script.bin or *.bin depends on the os.
Use bin2fex to convert the bin file to fex file. (If you don't have fex2bin, do "apt install sunxi-tools")
the fex file is just a text file, search for "[csi0]", it stands for Camera Serial Interface 0.
if you are using Orange Pi Zero Plus2 H3 board with OV5640 camera, you can use the following setting, if you are using a different board, you need to check the board schem