-- Open Windows File Explorer and browse to where your data is located. For most installs, this folder is located in C:\Users\<your login name>\Appdata\Local\N3V Games\trs19\.
The folder is named build-something. (The something is some sequence of letters and numbers).
-- Write down the name of the folder with the recent date on it, in case you have others in there.
If you still have the original TRS2019 download, you can reinstall that again directly, if not, you'll have to download TRS2019 from your My Trainz account.
Let the installer do its thing and even setup its own new data folder.
Once done, at the Launcher, click on Trainz settings.
-- Click on Install tab.
-- Click on the ... on the right side of the data path.
-- Browse to the data folder that belongs to your currently broken install, the one you wrote down
-- Click on the folder.
-- Click on Select.
TRS2019 will do a update translation-tables and will want to restart.
Once restarted, a DBR will run. This can take some time, depending upon how much data you have. If it runs really quickly, I'd be suspicious and check that the proper path was selected.