Hello JGC and thank you for reaching out. When you say: "It does not allow me to do that"? what do you mean exactly?
Assuming that you have installed the Datasmith plugin found here correctly.
You will find the Datasmith plugin, under the Datasmith tab in the top menu barre here :
To export from Revit using the Datsmith plugin, use the export to Datasmith file. If you want to connect Revit to Twinmotion using Datasmith, use the Connection button.
You can also find some articles regarding the installation and getting started with Datasmith here :
https://twinmotionhelp.epicgames.com/s/article/How-to-Install-Uninstall-Datasmith-Plugin-for-Revit-Windows-only
https://twinmotionhelp.epicgames.com/s/article/Datasmith-Exporter-Plugin-Installation-File-Paths-and-Accessing-Logs-for-Revit
https://twinmotionhelp.epicgames.com/s/article/Getting-Started-using-Datasmith-Workflows-with-Twinmotion
Please let me know if you have any other questions
cheers
MC