Thank you for reaching out. I understand you wish to abort the Azure Front Door migration process.
If I understand it correctly you are in the 2nd step "Prepare for Migration" where the premium profile has been created and now you have both Classic and premium profiles and you did not start the Migration process (3rd Step below).
In this case you can abort the process by clicking the abort migration button, which will delete the new front door profile created and existing profile will still remain active (refer the screenshot below). You can refer to this documentation for additional details.
You can follow this documentation to do this process via PowerShell.
Hope this helps! Please let me know if you have any additional questions or concerns. Thank you!
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