Restore Your iPhone
If you need to do a Restore to get your data back, first backup the iTunes backup directory. Do this so if something goes wrong during the restore, you have another copy.
Then, follow the instructions here to restore: http://support.apple.com/kb/HT1414 basically the steps are, you restore the iPhone, then restore the backup, then sync to get your apps back.
Note that one of the first steps of the restore process asks if you want to back up your data. This is for people who have an issue with their iPhone and are NOT trying to rollback to a previous version of the data. DO NOT select the BACKUP option during the restore, as this will overwrite the very backup you are trying to restore!
Restoring Just GPS Log
You can restore just the GPS Log data if you prefer. First, extract the GPS Log data from your iPhone's backup. You can use the iPhone Backup Extractor for Mac or iPhone Backup Extractor for Windows to accomplish this.
GPS Log data will be listed under a name like 'GPSLog' or 'com.williamdenniss.*'
Then use the FTP feature in GPS Log to upload the data to the iPhone.
If you have manually created a backup of GPS log via FTP then you can restore that backup the same way you created it.