Whilst TaxCalc has the ability to import filing details from the previous tax year (if the import option has been used), you cannot recover the HMRC password via TaxCalc as the password is encrypted for security purposes.
If you do not recall what this password is, you will have to reset this. There are two options on how to reset your password:
You can complete the password reset online via this link.
Call HMRC on 0300 200 3600 to receive a new password which will be issued by post.