The surveys are listed in the survey, but how I can select Multiple surveys at one time to generate one velocity SEGY volume from multiple surveys.

You’ll need to make a dummy survey in the Kingdom project that covers all the 3d surveys.  Ensure your grids cover the same area.  I’d make sure the inline/crossline spacing is quite large so the final volume doesn’t end up to be huge.  Then import that into the model as per the instructions before, and generate the volume for the dummy survey.

However, Kingdom will limit your use of this survey, but you will be able to visualise it etc.