In an opened KeyStore window, select the key pair entry and click on
the right mouse button. From the popup menu select Export > Export Key Pair
action.
The Key Pair will be exported in the selected file. The Key Pair can be
exported in PKCS #12 KeyStore Files format. Also, a PKCS #12 password is
required. While exporting a Key Pair, an error might occur if the password
length is too long - this has to do with the out of the box Java
Cryptography Extension (JCE) limited Strength Jurisdiction Policy
Files.
A screenshot for the export Key Pair action is depicted below: