Trezor's Shamir Secret Sharing uses SLIP39 and from what I recall, they are not interchangable. I'm assuming that you're talking about BIP39 seeds. If that is the case, then it is not possible. BIP39 uses PBKDF2 to generate the seed which is a non-reversible function and as such you cannot generate a seed from that. SLIP39 and BIP39 are fundamentally different so they are not compatible in the first place.
BTCrecover actually supports SLIP39. Refer to the documentation here:
https://btcrecover.readthedocs.io/en/latest/Usage_Examples/basic_password_recoveries/#slip39-passphrases.
I didn't know it supports SLIP39, thank you for the help, it works with that! I can just enter my SLIP39 seeds there.
Thank you and the thread can be closed now.
In general, you can't convert a master private key back into a mnemonic phrase (as ranochigo mentioned), because the alrogithms currently in use are all irreversible.
You might be able to combine the Shamir parts if they lead you to reconstruct the whole mnemonic phrase. But that depends on whether that is the contents of the secret parts.
Why would you need BTCrecover though, anyway? Have you lost some of the parts (or the Trezor)?
I forgot my secret phrase, but I remember enough of it that I should be able to crack it using BTCRecover.
