Migration Office 365 to Office 365

Hi Md. ShamimReza,

Generally, when we migrate Office 365 data between two tenants, we need to transfer mailboxes, SharePoint Online, OneDrive for Business data as well as custom domain(s).

You can refer to the following article for how to migrate mailboxes:
How to migrate mailboxes from one Office 365 tenant to another

For SharePoint Online sites, you can re-create the site collections in the new tenant. You may save the previous sites as templates (including the site content) and download them to your local PC , and then upload to the SharePoint Online of your new tenant. For the details, please refer to Create and use site templates. If some sites (e.g. Publishing site) couldn't be saved as templates, you may need to download the files manually and upload them to the new one.

For OneDrive for Business data, you can sync your data in your OneDrive for Business library to your local drive, back up the data to another location on your PC. After your OneDrive for Business service is available in your new tenant, sync the data back to the new OneDrive for Business library. Please follow the steps in "Test the feature before you enable it for your organization" part in this article to set up the OneDrive for Business sync client, use IE to download and then run the TeamSiteSyncPreview.reg in that article.  

For custom domain, you may remove it manually from the previous tenant and then add it to the new one. During the process, the users couldn't receive or send emails using the previous email address. It takes about 72 hours to complete it.

Regards,
James