SharePoint 2010 to SharePoint Online Migration Steps:
Step 1: Export the data from the SharePoint 2010 environment using Export-SPWeb.
Go to the start menu, and run the SharePoint 2010 Management Shell as Administrator
Now, run the following command:
Export-SPWeb -Identity “http://<On-PremSPSite>” -ItemUrl “/OnPremDocLib” -Path “C:\SPOnPremExport” -NoFileCompression -IncludeVersions 4
Note: Replace the Web URL and the Document Library with your own URL and Library name.
After completing it successfully, you will see that a folder has been created
Create a new XML file in the above exported folder with the name: LookupList