I apologize for any inconvenience caused.
Well, you can always use our premium add-on ATUM Export Pro. With this add-on you will be able to export any kind of data of your site, import it on a spreadsheet and then import it again to your site. In your case you can import your products, edit the prices in bulk and then import this CSV to your site.
I leave you here the link to the documentation of the add-on where you will find useful info about how it works: https://forum.stockmanagementlabs.com/t/atum-export-pro-documentation
And the link to the demo site if you want to try the free trial: https://www.stockmanagementlabs.com/addons/atum-export-pro/
In any case, how did you 'convert' your products to ATUM? It's weird that the prices didn't pulled across to ATUM and it's not the normal behaviour.