If the asset is in fact gone, as in deleted and sent to bit heaven, don't panic. There is a backup folder, you know.
The folder is located wherever your Trainz content is installed and has sub folders named for the day that you used TRS19. By default, the backup is created for 7 days that you use TRS19. These don't have to be consecutive and the oldest of the dates is deleted and the others remain until they pass their expiration date.
Open up your Trainz date-folder wherever that's installed. By default, TRS19 puts its data in your User/<login>/App Data/Local/N3V Games/TRS19 folder. The actual data folder name begins with Build and has a bunch of letters and numbers following that. You can get the exact folder name by going to the Launcher and clicking on Trainz settings then Install tab. You'll see the folder name in the white space. Jot down that name on a piece of paper.
Once you locate your backup folder and the day that the asset got deleted, you can now restore it.
The file will be the kuid name without colons
) like this kuid 2 124863 100250 2 (I made this up, so don't look for it) with a .tzarc extension.
.tzarc is a compressed file and can't be opened directly.
Copy this file to your Trainz editing folder which is also found under your content-folder.
Close or minimize explorer and run a database repair to restore the asset.
If there's a sequence of numbers after the .tzarc like this .tzarc6374, then remove the numbers by renaming the file but remember to keep the .tzarc extension.