Where can I swap my core?

Could you please clarify where exactly I can swap my core? I'm a bit confused about the available options and I'm looking for a reliable and secure platform to make the exchange. Do you have any recommendations? Are there any specific exchanges or marketplaces that are popular for swapping cores? I would also like to know if there are any fees involved and what are the general steps I need to follow to complete the swap successfully. Additionally, are there any safety measures I should take to ensure the security of my transaction? Thank you for your help!