Use Copy user permissions to replicate the permissions from a user to another user or multiple users.
You can replicate these permissions within tenants, farms, sites, lists, libraries, documents, and list items.
For example, you can use this option if an employee just moved to a new team within your organization, and you want to give him access to all the same sites as another member of that team.
Note: You can also copy permissions to and from SharePoint groups and security groups.
Prerequisites
You have site collection admin permissions on your targeted site collection(s).
Note: Site collection admin permissions are required even if you have higher admin privileges like SharePoint admin or Global admin permissions. For more information, see Microsoft administrative permissions.
Tip: To manage all your site collections, you can connect to your central admin or admin center with SharePoint admin, Farm admin or Global admin permissions.
Index
How-to
On the Explore screen, select the item(s) on which you want to copy user permissions.
Click Copy User Permissions in the Quick action menu at the right.
Select the user or group you want to copy the permissions from in the Select a source user or group field.
Select the users or groups you want to copy the permissions to in the Select the target users or groups field.
Check the options you want to apply to the copy.
Click Apply.
The task will now run.
In the case that there are warnings or errors, they will be displayed with details in separate tabs near Results.
Options
Copy group membership
Select this option to add the target user to all the SharePoint groups the source user is a part of in the selected SharePoint items.
For example, if your source user is part of a SharePoint group called Marketing in the site you selected, your target user will be added to the Marketing SharePoint group.
Apply permissions to all subsites, lists, and libraries with unique permissions
Select this option to give your target user the same permissions as your source user on all the SharePoint items with custom permissions within the SharePoint item(s) you selected on the Explore screen.
For example, if you select a site that contains a library with custom permissions and check this option, your target user will get the same permissions as your source user on that library.
Apply permissions to lists and library content
Select this option to give your target user the same permissions as your source user on all the list items and documents with custom permissions within the SharePoint lists or libraries that are part of your selection on the Explore screen.
For example, if you select a library that contains a document with custom permissions and check this option, your target user will receive the same permissions as your source user on that document.