I wanted to add new transition to existing workflow, it was not allowing to do in active workflow. I have then created the copy of workflow, made changes in the copied workflow and now wanted to Switch to the new workflow.
However the Switch Scheme and Associate buttons are not available to me. I have site administrator role and administrator role.
You can't switch the scheme of a workflow form the global administration.
To Switch the scheme you have to navigate to the Jira project > projects settings > workflows and there you should see a button "Use a different scheme"