Currently users can migrate DemandTools 2.91 scenarios from the Single Table Dedupe (Dedupe in DTV) & MassImpact (Modify in DTV) modules. This can be done by navigating to the Settings Wheel/Cogwheel > Migrate DT 2.91 Scenarios & Rules. Just keep in mind that if migrating Single Table Dedupe scenarios, you will need to migrate any associated Winner or Field Rules.
For the other modules I would suggest recreating those scenarios manually to get a head start on migration - if you have time, you can also login to https://my.validity.com/demandtools/products and submitting a feature request by following the steps outlined here.
