To create a new entry form an IACR eprint ID, choose BibTeX → New entry.... In the lower part, there is the box "ID-based entry generator". In the field "ID type", "IACR" should be already selected. The field "ID" is focused. Enter the eprints' ID here and press Enter to generate an entry based on the Id. You can also click on "Generate". The new entry is opened in an entry editor. In case an error occurs, a popup is shown.