How do I merge multiple OneDrive accounts?

Identify each OneDrive account
Sign in to the web version of each OneDrive account
If the accounts are associated with different Microsoft accounts, move the contents of each OneDrive account to a single Microsoft account
Open the OneDrive app and log in to the OneDrive account associated with the Microsoft account containing all the content
If you only need the contents of a single OneDrive account, delete the contents from the other OneDrive accounts online or within the OneDrive app
If all the content you need is in the same Microsoft account (one with multiple OneDrive accounts), delete the other accounts by selecting Settings > Manage Storage in the OneDrive app.