How to git pull merge to a new branch?

Hello,
I want to create a pipeline which fetches any new release of a repository and merge it my own repository, but I’m stuck on the push step. To be honest I don’t fully understand the git “put” step and if it’s possible to create a new branch with it ? Here’s a snippet of my code:

   resources:
  - name: github-stratos
    check_every: 20s
    type: git
    source:
      uri: 'https://github.com/cloudfoundry/stratos.git'
      branch: master
      username: ((blabla))
      password: ((blabla))
      tag_filter: '*'
  - name: stratos-myrepo-git
    type: git
    source:
      uri: 'https://myprivaterepo/_git/stratos'
      branch: release/3.1.0
      username: ((blabla))
      password: ((blabla))
jobs:
  - name: Run Check Script
    public: true
    plan:
      - in_parallel:
          - get: github-stratos
            trigger: true
          - get: stratos-myrepo-git
      - task: Check for new version
        config:
          platform: linux
          container_limits:
            cpu: 2
            memory: 4gb
          image_resource:
            type: docker-image
            source:
              repository: avarteqgmbh/blabla
              tag: latest
          inputs:
            - name: github-stratos
            - name: stratos-myrepo-git
          run:
            path: sh
            args:
              - '-exc'
              - >
                cd github-stratos

                tag_version=$(git describe --tags)

                cd  stratos-myrepo-git

                git checkout -b "${tag_version}_test"

                git remote add upstream
                https://github.com/cloudfoundry/stratos.git

                git fetch upstream

                git pull --no-edit upstream $tag_version

                git add --all

                # git commit -am "Merging the new tag version"