how to selectively merge with git?

in IDEA, everytime I click "merge into current branch", it merges all submits from that branch to my local branch.

But image this case: I have two branches, A and B. A's jdbc file is set to connect to the production database, and B's to dev database. I don't want A to connect to the dev database, nor B to the production databse.

So now when I commit the jdbc file in B branch, and I commit some other changes in B branch. then I would want to merge the "other" changes from B to A, but not the jdbc file. What should I do?