Migrated password hashes support

Hi everyone,
I have been trying to migrate from vBulletin to Discourse. I was following this link to do that: Importing from vBulletin 4
I updated the import script to copy over the password hashes and salt from my vBulletin DB to Discourse DB. The database has been successfully migrated.

The problem I am having is that the old users are not able to log in due to different password hashing scheme followed by Discourse. So basically copying over those password hashes was futile.

Then I came across this plugin which would convert my old hashes to the ones that Discourse uses.
After installing this plugin, I am still not able to log in using an old user.
I am not sure where to make make the suggested change for this plugin to work:

user = User.find_by(username: 'user')
user.custom_fields['import_pass'] = '5f4dcc3b5aa765d61d8327deb882cf99'
user.save

Can anyone guide me with this?

Thanks in advance.