Passwords that get set affect FUTURE backups that get created. If you're trying to access an existing backup, you need to know the password that was used to create the backup in the first place, because the password is the derivation for an encryption/decryption key. You can't just set a new one in Reflect and expect that to work retroactively to access data encrypted under a different key. I would also strongly recommend that you do NOT specify a password under Edit Defaults, because that will be applied to ALL future definition files you create (and any backups you create without a definition file) unless you remember to change or remove that password when setting up the job -- which means you're more likely to end up in this predicament again because you might not even realize a backup you created was password protected until much later when you tried to restore it. Instead, create a definition file, and in the Advanced Options of that specific definition file, specify the password you want to use for backups generated by that specific job. But passwords set in Edit Defaults or Advanced Options don't come into play during restore scenarios; again, they only come into play when future backups are being created.
If you forgot the password of previous backups, then your data is effectively lost. There is no "I forgot my password" function in Reflect or almost any other tool that uses local data encryption, because having that "escape hatch" requires you to give some other entity your password or some other ability to decrypt your data. Microsoft and Apple offer this with BitLocker and FileVault, respectively, but since that of course introduces security and privacy concerns, those features aren't used by default even there, and I think it's fair to assume that Microsoft and Apple have much larger cybersecurity budgets than Macrium and therefore might be in a better position to store sensitive user data like that, whereas Macrium might specifically not want that responsibility even if some users wanted them to have it. And that's before considering that storing that type of user data would mean Macrium could potentially end up embroiled in legal conflicts where someone tried to compel them to release that information, and again I suspect Macrium's legal budget is rather smaller than Microsoft and Apple's.
Obviously this doesn't help the current situation, but going forward, if you don't like the idea of writing a password down as @Drac144
mentioned (though there is admittedly a case for writing things down on good old paper as long as it's secured somewhere), I personally use LastPass for things like this. I was using it anyway to manage my website passwords, but it has a Secure Note feature that allows you to create arbitrary text files that also get stored and synced to the cloud, although the syncing is done in such a way that even LastPass can't decrypt your data, which is why I'm ok using it. It's also got some other handy features like Emergency Access, which is designed to resolve the quandary of keeping your information confidential and secure while you're alive but making sure your loved ones (or whoever) can get access to it if you're unexpectedly incapacitated or killed, without having to resort to paper that can obviously become outdated. LastPass has a nice solution to that.