In order to void a ticket from a split PNR, you need the following information (and please make sure to always first go out of the PNR, otherwise it won't work):
- date of issuing

- ticket number

- IATA number


Go out of the PNR and use the following entry:

DDV*17JUL00112345678#N1.1*5720146


Or in case of conjunction tickets, use:

DDV*17JUL00112345678-679#N1.1*5720146