Yes, you will need to mail in an amended tax return. Amended tax returns cannot be e-filed.
Also, to prevent
fraudulent returns, the IRS will only accept
each dependent's SSN once in their e-file system. Because you filed
first and used your SSN, no further e-files using that SSN will be accepted. Whomever is claiming you as a dependent will need
to print, sign, and mail in their tax return.
Their return will be accepted if you amend your return and they mail in the tax return.