If you don't know the password, then the data is effectively lost. There's no master password within Windows or Reflect itself or any sort of reset/forgotten password mechanism. If you think you might remember your password later, it would be worth keeping those backups for a while, but you should absolutely start a new backup set with a known password right away.
Also note that changing the password and encryption settings in Edit Defaults only affects brand new definition files
created after the change. It will not change the password on any existing definition files (even if you subsequently make other changes to them), and it certainly wouldn't change the password on any actual backups you had previously created. I personally would recommend against setting a password in Edit Defaults because if you ever create a one-off backup, that password will be applied and you might not intend that or remember the password later. If you want to change the password for a definition file you're already using, go to the Backup Definition Files tab, right-click the definition file that runs your job(s), select Edit, click Advanced Options, and change the password there -- and then create a new Full backup, because Diff and Inc backups always maintain the password of the existing backup set. If you want to change the password of existing actual backups themselves, Macrium does not provide a way to do that even if you know the current password.
Going forward, you might want to consider a password manager like LastPass. I use it primarily to manage my website passwords since it operates as a browser plugin, but it can also store "Secure Notes", which can be arbitrary text and are therefore useful for storing non-website passwords or any other sensitive information. LastPass implemented their security properly such that even they can't access your vault data, which means they can't directly reset your password. Instead, your recovery options are rather limited (documented here
). But of course you only have to remember one password with them in the first place if you have everything in there, so hopefully forgetting isn't as much of a risk. Just make sure it's a long, unique password since it will protect everything else. And the paid version has a feature called Emergency Access which I think is an elegant solution to the, "I want to keep my data private, but what if I get hit by a bus and now my family needs access to it unexpectedly?" problem.