You can use the clear ipv6 pim commands to reset PIM counters and mappings.
clear
ipv6 pim interface
Use to clear the counters for multicast packet statistics
on all interfaces or a specified interface.
Specify an interface type and identifier, such as atm
3/0 to clear the counters on that interface. For details about interface
types and specifiers, see Interface Types and Specifiers in JUNOSe Command Reference Guide.
If you do not specify an interface, the router clears
the counters on all interfaces.