Unfortunately, if you do not know the password for an AxCrypt-encrypted file you cannot open it, even if you can sign in to the account. This is by design, it’s just this situation that AxCrypt is made for and it works like this even if you actually are the original owner of the file.
So please try to remember the file password(which was used in the encryption process) to decrypt/open the old encrypted files.
If you do not remember the password to your account, you can always reset it. This is not a way to recover encrypted files! It’s only to allow you to sign in to the AxCrypt app and web. The new password will be used to encrypt new files. Go to https://account.axcrypt.net/Home/PasswordReset to do this, or you can also go there from AxCrypt with File | Options | Password Reset.