In order to work with the Gift Adjustments data destination in Importacular, you will need to work with a data source. Often, with this destination, this is a File (.csv or Excel - .xls or .xlsx) which you can create in the Raiser's Edge using a Query or an Export.
In order to import the Gift Adjustments you will need the following fields (at a minimum): Constituent information to identify the Constituent record (such as the Constituent ID, First Name, Last Name, etc. - if you do not have the ID, you will likely need an address or email address as an identifier), Original Gift information so that you can match to that gift (such as Gift amount, Fund, Date, etc.) and the fields that you want the data to be adjusted to (such as Adjusted Amount, Adjusted Fund, etc.).
Please note that, as of version 5.4, you cannot import adjustments to split gifts (see this knowledgebase article).
For more information about importing with the Constituent ID, please see this knowledgebase article.