A 64 character private key should be in hexadecimal format and include 0-9 and A-F characters.
First you should convert your hex private key to WIF. To do so, you can use bitaddress.org.
Just Note that it's not safe to enter your private key on an online website and it's recommended to run the offline version of bitaddress on an air-gapped device.
After deriving the WIF private key, you can import your private key to a wallet and spend your fund. A good option is electrum and note that it's recommended to run electrum on an airgapped device.
click
here to read the guide on how to make a transaction offline.