Oracle 9.2 - Bring standby up-to-date using RMAN
I do not have access to a 9.2 database currently, but this is the method for doing this:

Using RMAN Incremental Backups to Roll Forward a Physical Standby Database

Basically, you can issue a BACKUP INCREMENTAL FROM SCN ... to create the desired backup. However I suspect this feature is not available in versions before 10.2.0.1, as there is no reference of it in the 9.2 Data Guard documentation nor the 9.2 BACKUP reference, and the related MOS notes also specify the lowest version as 10.2.0.1.

Try the above syntax, but if it does not work, you will need to rebuild the standby.