Op every Bitcoin address has it's own special seed phrase. The seed phrase is a series of 12 , 18 or 24 words as the case may be, which is generated simultaneously along with the wallet address. The seed phrase in turn is used to create a private key known as the master private key and for the case of an HD wallet, that Master private key is used to generate child keys for other addresses.
I think your further explanation of this thread actually counters your own point in the first sentence, every address doesn’t have a specific seed phrase rather a single seed phrase can be used to generate multiple child private keys as you stated which in turn can be used to generated different bitcoin addresses. With a single bitcoin seed phrase you can even have addresses of different formats just by creating new wallets and specifying the derivation path you wish to have it. This is what I think OP is trying to do maybe get a bech32 address from his existing private key or seed phrase which he will just simply change in the options when creating a new wallet with same seed phrase