Open the Activities overview.
Click and drag the window to the workspace partially displayed on the side of the screen.
If more than one workspace is already in use, you can also drop the window onto one of the non-adjacent workspaces in the workspace selector between the search field and the window list. This workspace now contains the window you have dropped, and a new empty workspace appears at the end of the workspace selector.
Press Super+Shift+Page Up to move the window to a workspace left of the current workspace on the workspace selector.
Press Super+Shift+Page Down to move the window to a workspace right of the current workspace on the workspace selector.