These steps may help you regain access to your account: https://goo.gl/v7CdWx . We recommend doing this from a known device and/or browser that was typically used to access the account. Here are more tips to help you through the process: https://goo.gl/QtskMp . Keep us posted.
If it's a legacy channel, you need to link it to a Google Account to access it. Here's how: https://goo.gl/z8YXdy . Also, if you don’t remember your old YouTube password, unfortunately there is no password recovery option for these accounts. (1/2)