Git - choose which base to use in merge -

There are two types of merge chairs for merge me

  kevins-mbp : TAMenuApp Kevin $ GIT Merge-Base - All Dev_bield v3_merge 0c16efd68f4defa7bd39f092a631691ace269a9d 70f568259b4cc7b110f5c390ac93a8a4d721f27c  

Which of these IDs is a way of choosing cherry to use as the basis for this merge? I'm actually trying to use it, which causes this error when trying to do this error:

  kevins-mbp: tamenuapp kevin $ git-imerge merge dev_build u Do not do 'v3_merge' and 'dev_build'  

There is a unique merge base, so I'm asking to be able to decide which base to use.