If you are talking about the random bits, or entropy, you can use the bip39 tool above to get the words.

If you are talking about the xprv, yprv, or zprv that results from the mnemonic phrase, that is not possible. The entropy stored in mnemonic pharse is put through a hashing algorithm to generate the private key. It is one way only. (https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#from-mnemonic-to-seed)

Similarily, for any of the private keys of the addresses generated by the seeds, there's no way to get the seed from any of them.