When a workspace is created, the relevant boards, repos and pipelines are added as part of that process (see Workspaces article). You are also able to amend the settings of the workspace at any point by clicking on Workspace settings in the left hand pane under Manage Dashboards.
When clicking on Workspace Settings you will see this screen and you can: -
rename the workspace
change the category
add / remove boards, repos, build pipelines, deployment pipelines (note: this is dynamic and depends on the integrations your organisation has connected to Plandek)
delete the workspace
Remember to click Save Changes when you have finished making the amendments.