I have pushed some changes to a remote branch on Heroku, I need to merge this branch to my master branch on Heroku to trigger a new build of the app. Can this be done? Can this be done using Heroku-cli?
Heroku isn't a version control hosting service so you won't be able to perform a merge between branches you've pushed to Heroku. Only pushes to the master branch on your heroku remote will be built. If you need to push a local, non-master branch you can do something like this: git push heroku local-branch:master to trigger a build. They have documentation for this here.