MyLog is a historical record of what you have picked up live and the data comes from what was in the main (NavData) database at the time, so editing the main database won't affect what you already have in MyLog.
However, try MyLog > Tools > Populate as this looks at the main database to see if it can populate the records in MyLog. I don't know if it will work if you already have some aircraft details in MyLog though. It will populate "empty" MyLog records.