Your seed phrase will generate the private keys. Import your seed phrase on Electrum, Sparrow, Specter or Bluewallet and use any of the wallet to sign a message.
If you still want to use iancoleman, you have to change the derivation path from BIP44 to BIP84 and you will see your address and the private key.
https://www.talkimg.com/images/2023/09/01/MxtR8.jpegFor security, do not use iancoleman online website, download it offline to use on a word editor.
