Creating pointers to keys on SmartCard

I am new to OpenPGP and SmartCards but I cannot find how to do a fairly straight-forward task.

I am trying to sign a file with a private key stored on a YubiKey device.

Here is my session:

$   gpg --card-status Reader ...........: Yubico Yubikey 4 OTP U2F CCID 00 00 Application ID ...: D2760001240102010006096334120000 Version ..........: 2.1 Manufacturer .....: Yubico Serial number ....: 09633412 Name of cardholder: [not set] Language prefs ...: [not set] Sex ..............: unspecified URL of public key : [not set] Login data .......: [not set] Signature PIN ....: not forced Key attributes ...: rsa2048 rsa2048 rsa2048 Max. PIN lengths .: 127 127 127 PIN retry counter : 3 0 3 Signature counter : 3 Signature key ....: B692 4360 F06A AB92 1B9A  3E6D 3850 24E1 EE26 F6D9   created ....: 2019-05-14 14:44:27 Encryption key....: [none] Authentication key: B692 4360 F06A AB92 1B9A  3E6D 3850 24E1 EE26 F6D9   created ....: 2019-05-14 14:44:27 General key info..: [none] $   $   gpg -K $   $   gpg --list-keys $   $   gpg --with-subkey-fingerprint -K $   $   gpg --refresh-keys $   gpg --list-keys $   

I looked at some posts like this one: Create backup Yubikey with identical PGP keys but I am still not sure what I am doing wrong.

All I need to is somehow use the signature key to sign a file via

gpg --sign -u <key-id> somefile.txt 

I need to somehow create a pointer in my local keyring to the Signature key and figure out its id.

I am using gpg (GnuPG) 2.2.12 and libgcrypt 1.8.4

Any suggestions?

Thank you in advance!