@Maninder Kaur Sorry for the inconvenience caused!
Based on the information provided, I understand that you're experiencing an issue with the Azure Migrate tool where you are unable to select the VMs to migrate. please follow the steps suggested below:
Ensure that all required fields are filled out correctly. Sometimes, the 'Next' button won't activate if there's missing information.
Try clearing your browser cache and cookies or try using a different browser to see if the issue persists.
Make sure that your account has the necessary permissions to perform the migration. If your permissions were recently changed, it might take some time for the changes to propagate.
Look for any validation errors or messages on the screen that might indicate what needs to be corrected before proceeding.
Ensure that your network connection is stable. Sometimes, network issues can cause the portal to behave unexpectedly.
If none of these steps resolve the issue, you can use this link - https://portal.azure.com/?feature.customportal=false&feature.canmodifystamps=trueµsoft_azure_migrate=migratecanary#view/Microsoft_Azure_Migrate/AmhResourceMenuBlade/~/getStarted should help you resolve the issue.
If problem persist, contact Azure technical support by raising a support request. The ticket enables you to work closely with the support engineers and get a quick resolution to your issue.
Hope this helps!
If the response helped, do "Accept Answer" and up-vote it