Segment doesn’t have the ability to “merge” workspaces, however you can achieve the same effect by moving your existing sources to a single workspace.
You can move sources between workspaces by clicking the sources tab in the top left of your workspace,
heading to “Settings” for the requisite source,
and then clicking on “transfer to workspace,” selecting which of your other workspaces you’d like to transfer the source to.
You will need to ensure that the transfer is done by someone who is an owner of both workspaces.
You will additionally need to configure desired destinations in the workspace that the source is now sending data to.
Benefits of doing this include unifying all of your data across your team(s) to better track your customer data as a complete picture.