If you don’t remember who your current registrar is, you can look it up by performing a WHOIS search on your domain.
Make sure to set this email as your contact email in your domain registration information.
You will need this code in order to transfer your domain.
You may need to contact the registrar’s support staff to initiate a transfer if there is no option available on the website.
This is where having the correct contact information is important. If you are not registered as the owner of the domain, you will not be able to be contacted about the transfer even if you are the actual owner.
The actual process will vary depending on the registrar you choose. This may include an extra round of authentication from the new registrar. Check the support pages for the new registrar for details.