Hello @Jaswanthi
there is not OOTB way available to migration classic master page into modern. Customizations in modern are not suppoerted - see first article below.
Here are 2 articles about the topic:
Supported customizations for "modern" pages
https://learn.microsoft.com/en-us/sharepoint/dev/solution-guidance/modern-experience-customizations-...
The number of customizations available for "modern" pages keeps on growing, and in this article, we'll provide details and examples of the supported options. The SharePoint team is working to support more options in the future. The following list gives a quick overview of the supported capabilities for "modern" pages:
- Custom branding
- Adding "modern" pages programmatically
- Adding, deleting, and updating client-side web parts on "modern" pages
- Alternative layouts (see note on SharePoint Virtual Summit)
These customizations are currently not supported for "modern" pages:
- Adding "classic" web parts on "modern" pages
- Custom CSS via AlternateCSSUrl web property
- Custom JavaScript embedded via user custom actions (see note on SharePoint Framework Extensions)
- Custom master pages (more extensive branding will be supported later using alternative options)
- Minimal Download Strategy (MDS)
- Modern pages inside of the a Site Template package (Save site as a template)
Note
- We don't support combining "modern" page functionality with "classic" SharePoint publishing portals. By default, the "modern" page functionality is not enabled on "classic" SharePoint publishing portals.
- In June 2017, SharePoint Framework Extensions went into developer preview. Using these SharePoint Framework Extensions, you can control the rendering of a field via custom code, and you can create user custom actions that execute your custom code. To learn more, see Overview of SharePoint Framework Extensions.
Master pages, the Master Page Gallery, and page layouts in SharePoint
https://learn.microsoft.com/en-us/sharepoint/dev/general-development/master-pages-the-master-page-ga...
Find links to information about using Design Manager to work with master pages, page layouts, and display templates in publishing sites in SharePoint.
Important
This extensibility option is only available for classic SharePoint experiences. You cannot use this option with modern experiences in SharePoint Online, like with communication sites. We do not recommend using classic experience or these branding techniques anymore.
Best regards, Dave
