You don't "show" anything to anyone. However, you will be asked for personally identifiable information (such as your SSN, DOB, etc.) to prove to the website that you are, who you say you are.
My kids father is trying to carry my child&he used turbo last year. So that means he can file with her again??? This isn't fair. He didn't take care of her at all
If you "really" qualify to claim the child as your dependent, then do so. If you are unable to e-file because he was claimed on another tax return, then print, sign and mail the return to the IRS.
When the IRS sees that the child has been claimed on two tax returns, then both of you will be audited by the IRS. If dad does not qualify to claim the child, then dad will lose and dad will be the one paying fines, penalties and back taxes for filing a fraudulent return.