There are two ways to retrieve a GRIB file that has been deleted.
if you haven’t yet quit LuckGrib, you can use Undo to bring the file back. Simply invoke the Undo menu item from the Edit menu. If you have modified the model multiple times, you may need to keep invoking Undo until you come to the modification which resulted in the file being deleted.
if you deleted the file and quit LuckGrib, then there is no way to gain access to that file - its gone.
If the file was the result of a download within LuckGrib, you can download the file again by opening the GRIB Request window, selecting the relevant request and submitting it again.
When re-submitting this request, you may run into an issue where the application doesn’t let the request to proceed. LuckGrib keeps track of the time each request was last submitted, and if the server does not yet have new data available for the request, it will alert you to that fact - that the data you previously downloaded is the same as what is currently available. In this case, in order to download data that has been deleted you will need to fool the app into thinking you are downloading new data. Open the window to edit the request and modify it in any manner, and then Undo to return the request to its previous state. At this point LuckGrib will consider this request to be modified and will allow you to download data for it again - in effect, you have downloaded the exact same data twice, but as you deleted the first copy, this is what you want.
Of course, this is all easier if you simply don’t delete files by accident. LuckGrib is able to easily track and deal with many hundreds of files. With our storage devices being many hundreds of Giga-bytes large and GRIB files being relatively small - perhaps just keep them all!