I have not used the 833, but here is a sample program illustrating the use of the R_Trig instruction. Basically,
the program uses a Timer to increment a variable as long as the .Q bit is energized and it uses the .Q to trigger the R_Trig instruction, so the variable Count_2 only increments one time. Notice that the instance of the R_Trig must be declared in the varaiables declaration for the code to work.
You should be able to open this with CoDeSys and run the program in simulation mode.
Regards