SharePoint Online:How to do Move Site and subsites into another site?

•  http://yoursite/_layouts/sitemanager.aspx", 
• Go to site manager option
• Select the parent site of the subsite you want to move in the left navigation pane.
• Check the box next to the subsite you want to move in the right pane.
• Click Actions drop-down and click Move.
• Select Destination of the subsite selected in the next dialog

Or 

We can use the Tool SharePoint Migration Tool, ShareGate or Content Matrix trail version