To set Force push permission for a branch, it’s located in Branch Security. If you are an administrator for the team project, you can also set it by yourself. Detail steps of setting as below:
In the VSTS team project -> Code Tab -> selected the repo you are working for -> Branches Tab -> select the branch you want to set force push permission -> … button -> Branch Security -> set the group you are in or add your account as user -> set Force push to Allow -> save changes.
