If you're a member of a space, you can move any thread in that space to another space that you're also a member of.
Everyone already on the thread, and anyone in the space you move it to, will be able view, edit and respond to it.
To move a thread:
- Go to the thread
- Click ... on the top-right corner of the thread
- Select Move Thread
- Add the space you want to move the thread to
- Click Move
