Copying Files from One Document Library to Another with Explorer View
This article discusses how to use the Open with Explorer command in SharePoint Online to view, copy, and move files in a library.
From time to time, you might need to copy or move one or more documents in a library to another library. For example, you might want to move all documents created over a year ago in one library to another library. Or, you might want to copy documents from a library that you own from one site to another library in a subsite. To do these operations, you can use the Open with Explorer command, which is an additional way to manipulate files in a SharePoint library. When you use this command, it opens Windows Explorer on your computer, but it displays the folder structure on the server computer that underlies the site. You can manipulate the files in the folder, such as copying, renaming, deleting, and so on.
Copy or move library files
The following sections show you how to move or copy files in a document library from one site to another site. Click on red mark icon and then wait to open the explorer window in few secs.
The window looks like this so you can select documents, pictures, or any type of documents.
And open target window as same as source folder and paste it.