You can choose any of the secondary nodes to perform backups of MongoDB replica sets and sharded cluster deployments.
From the navigation pane, go to Protect > Big data.
The Big data page appears.
In the Name column, click the cluster that you want to modify.
The cluster page appears.
On the Nodes tab, do the following:
Click the check box for the secondary node that you want to use for backups.
Click Set as data access node.