How do I revert to a previous ROM?

[mrkiii]

Hi dear
I've installed a ROM on the phone. Now I want to install the previous rom, but I'm faced with this picture
I tried several times with different ROM
huawei g6-u00

 

[UJ95x]

Welcome to AC
You need to have made a nandroid backup to return to a previous ROM in the state that you used it in.
You should still be able to flash a ROM through your custom recovery. It's hard to tell, but are you using ClockWork Mod?