Hello @sunil1. It does take time for the primary domain change to complete, so if you changed it then immediately tried changing it back then it may just have not been available yet. Or check if it's an add-on domain that's already set up on another hosting plan and remove it. If neither of those are working then reaching out to live support via phones or chat would be best so they can check for any account specific issues.
Naterx - GoDaddy | Community Moderator 24/7 support available at x.co/247support