Plus (+) icon is not visible if you already selected build and you just half process got done.
in that case you just edit your existing in-progress pending process:
Steps to done it:
-> go to apps
-> click on existing application which you want to upload new version
-> select last version
example:
iOS App
1.3.4 Waiting for Review <----------
1.2.6 Ready for Sale
-> do here what you want like cancel for
-You can edit some information while your version is waiting for review. To submit a new build, you must remove this version from review.
-remove old build file and select new one
that's it.