The m prefix is a SI prefix denoting milli, or one-thousandth of a known value.
Thus, 1 BTC = 1000 mBTC, or 1 mBTC = 0.001 BTC.
You appear to have 0.83 mBTC, which is 0.00083 BTC, or about 6 USD at current rates.
The fingerprint of a public key is defined in BIP 32 as the first 4 bytes of the RIPEMD160 hash of the SHA256 hash of the public key. The fingerprint of a particular xpub can be gotten from that xpub, but this is not useful information.
What the Coldcard wants is the fingerprint of the master xpub. It wants the fingerprint of the key at derivation path m. ...