HODL can be mined using specialized mining software. XMR Stak is a commonly-used mining tool that works for CPU mining and GPU mining with both Nvidia and AMD graphics cards. CCMiner is another popular mining tool for computers with NVIDIA graphics cards. In addition to having mining software, you will need a HODL and access to a mining pool that pools your effort with other miners and a wallet to store the HODL that you earn from mining. Most cryptocurrencies have multiple publicly-available mining pools that can be found with a simple Google search.