CBR vs VBR setting in Media Encoder for Amazon Video Direct

Greetings,

     I have a video file that I uploaded to Amazon Video Direct. But they found a couple of problems with it.

     They said that the Video uses VBR. But that they only accept CBR.

     If I choose the H.264 Preset, then I see a choice to select VBR/ CBR.

     However, I'd like to use the ProRes 422HQ preset, but when I select this, I didn't find a Setting that allowed me to choose CBR (instead of VBR), or for that matter the Bit Rate.

     Any idea on how to achieve this?

      Thanks in advance.

Regards,

Rajnesh