tonytony - Be assured that your efforts to install this app will eventually be handsomely rewarded. TRS19 is a fantastic railroad simulator, so it is definitely worth persisting.
As clam1952 asserts above, Content Manager is your friend! Use the 'Faulty' filter and 'Open for edit' filter to resolve any missing assets/ dependencies.
Create two new custom query filters that you will probably run daily as a prudent maintenance action:
1. An 'Out of Date' query that will identify any recent updates to your installed assets, whether built-in, or from the DLS or DLC. (Installed=True and 'Out of Date'=True)
2. An 'Obsolete and not Built-in' query that will allow you to delete obsolete assets from your database. (Installed=True, Built-in=False, Obsolete=True)
After an initial installation, you will often need to download and install additional routes and sessions that are included in your version of the product by downloading them from a list presented to you after running the Launcher for the first time.
Run a Database Repair to ensure the integrity of your recent installation. (Developer menu in Launcher, "Rebuild database').