If you need to back up specific databases, you can do so by creating a user-defined subclient.
From the navigation pane, go to Protect > Applications > Office 365.
The Office 365 apps page appears.
Click a SharePoint server.
The selected SharePoint server page appears.
In the Contents section, click the Office 365 backup set.
The Office 365 backup set page appears.
Click Add subclient.
The Add subclient page appears.
Type a name for the subclient, and then select a plan.
To add content to the subclient, complete the following steps:
Click Add content.
The Add content dialog box appears.
Select one or more sites that you want to add to the user-defined subclient that you are creating.
Click Add in the Add subclient page.
Note: You cannot have a library as subclient content. You can have sites or site collections as subclient contents.
The new user-defined subclient appears in the Add subclient page, under the Subclients section.