Gail:

Do you mean a backup created using the File | Backup option in Ledger? If so, do the following:

Note that the steps aren't difficult but you must be very careful about file names & locations.

For this explanation I will assume the following:
=Data folder is X:\ASP\DATA (yours will be different)
=Data extension is DAT
=Your most recent GL backup is the one you want to restore.

-Start Ledger
-Go to File | Backup | Backup Options
-Note the field named "Next Sequence" & subtract 1
-For instance, if you see 6, your backup file is named BKGL0005.zip
-Exit from Ledger
-Browse to the X:\ASP\DATA folder
-Make a new subfolder named GL08JAN21
-Select all of the files starting with GL and a file extension of DAT
-Cut those files and Paste them into the GL08JAN21 folder
-NB: Cut & Paste, not Delete
-Browse to X:\ASP\DATA\DATABACK
-Locate the filename that you determined earlier (BKGL00xx.zip)
-Extract JUST the GL files into the X:\ASP\DATA folder (be careful here!)
-There shouldn't be any GL files so there should be no overwriting
-Start Ledger & immediately use File | Data Integrity Check
-Redo any work completed since the backup was originally created.

Note that if you retrieved any subledger batches after the backup was made, you will need to manually input those batch(es).