Converting a C25519 curve into a NIST-supported curve for FIPS crypto
No, conversion of an EC key pair from a curve to another of unrelated order is not possible.

One of the closest things that could be done would be that parties generate a new P256 key pair, then


certify their new P256 public key using their C25519 private key, check the other party's certificate using the other party's trusted C25519 public key, and now trust the other party's P256 public key.
or negotiate trusted symmetric session key(s) per their C25519 key pairs, and transmit their new P256 public key over a channel secured by symmetric crypto.