If a CA Panvalet control code is lost, is there some way to reset the control code without knowing it's current value?
No. That would be considered a security vulnerability.
If you have a PANLIB that requires a Control and don't know what it is, run this IDCAMS dump job -
//IDCAMS EXEC PGM=IDCAMS
//INDD DD DISP=SHR,DSN=hlq.mlq.PANLIB
//OUTDD DD SYSOUT=*
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
PRINT INFILE(INDD) DUMP COUNT(3)