You can't "fix" this except by printing your correct return, signing it, and mailing it in. The IRS will process your return and pay your refund, and then address any conflicts.
If you did figure out which dependent was the problem, and remove them so you can e-file, you may get much less money, and then it would take 6-8 months to get an amended return with the correct info.
If you claimed the correct dependents based on the rules, file by mail. If you think your child might be a victim of identity theft, you can get an IP PIN for them that will block anyone else from claiming them in the future.
https://www.irs.gov/identity-theft-fraud-scams/get-an-identity-protection-pin
