I have done several Omron HMIs, but I am not familiar with the NT3. Nor did I have any luck on Google. Do you have a more complete Model Number? I assume you are using NTST the NT Series Support Tool to program it?
I haven't worked on one of those, and I don't have the NTsx Software.
The Link to the manual posted by Bluebyu does have a section on setting up alarms, so start there.
Hopefully, someone with experience with them will show up.
I've got it! all very easy i just had to set the alarms as a HR/IR word and the alarms are then the the coil addresses EG :- 10.00 alarm 0 , 10.01 alarm 1 and so on. I was over complicating as usual !!!