Covert a DES 96 bit key to 64 bit

How can I convert a 96 bit key to a 64 bit key? I have a DES key that is 96 bits long (i.e 745347651281) . I want to convert this to 64 bit which I will use to decrypt a DES ciphertext.

Update:

1. There was an "original key" encrypted by RSA
2. The "original key" was decrypted using RSA to give us this (i.e 745347651281)
3. This (i.e 745347651281) is now supposed to be used to decryped a DESfile.

Note : The "original key" was in hex format which I converted to integer(base 16) before doing RSA decryption.