If you've put in a *.gdb folder, don't. In fact never put anything into a .gdb using non-ArcGIS tools. They're a geodatabase, not a folder and ArcGGIS won't see any non database files in there.
If you didn't actually copy them into a .gdb, but into a non gdb folder, then you may just need to right click the folder (from within Pro, i.e using the catalog pane) and select refresh