Dotted RTL how to use

[my_only_lonely]

I have read the doc https://wiki.freepascal.org/FPC_Dotted_RTL, and compiled a new RTL. But how can I use this version of RTL, is there any switch I should add?
Lazarus still cannot compile when uses a dotted unit, like System.Generics.Collections, it says it cannot find the unit.

[PascalDragon]

You need to make sure that the fpc.cfg of the compiler that Lazarus uses points to the correct RTL (maybe even with a separate ifdef so that you can relatively easily switch between dotted and non-dotted RTL).