Follow the steps to implement
Go to Office365.com and sign in with Admin credentials.
Now, navigate to Setup in the menu and select Data Migration.
select Data Migration
On clicking Data Migration, the “Select your data service” dashboard will appear on the screen. If your email provider is listed in it, then select it.
Select your data service
After selecting the email provider, you will be redirected to select users.
Select the email provider
Select the users that you want to migrate and fill the email alias & password.
Click “Start Migration” at the left corner of the wizard after entering the required information.
Click Start IMAP to Office 365 Migration
The migration status will be any of these: Starting – Queued – Syncing – Synced. When the status comes to Synced, click “Stop Migration” to finish the process. Once the process is complete, click “Close Connection.” Get to know more about in detail.
I hope this method will be helpful!