If classes were not utilized with assets when entered or the class needs to be updated, this can be done within a few steps.
Access an asset via the assets master list menu option
Click on the Class field in the primary info panel of the asset
Select from the available classes in the drop down
Click the checkmark to save the changes to the class field
If needing/wanting to update the class on multiple assets in bulk, the import/export utility can be used via the Classic application. Refer to Import/Export Utility for more information.