Both successful and failed workflows can be rerun, either:
From the workflow page
It is the page you are looking at when you look at a graph of jobs.
At the top right of the page, there is a "Rerun" workflow button. Click this button to reveal a menu, where you can choose to rerun the workflow from start or from the first failed job:
From the Pipelines page
Please note that rerunning a workflow will use the exact same processed configuration as the initial workflow.