If all you are interested in is the dead rock (not live rock) then bleach the rock, then rinse very well, then sit it out in the sun for a day. However, now it would be dead rock. It would be dead rock too if you just set it in the sun. You have to really sterilize the rock to make it safe for the tank, otherwise it will contain die-off that remains on the rock (which will cause problems for your tank).
If you want to keep what is living and make sure it is pretty safe, keep it QT-ed for 3 weeks at least. While in QT, you can check for undesirable things such as aiptasias, which would be highly beneficial to get rid of before you introduce your rock to your tank.
Check out this topic to see what I mean. This hobbyist could have avoided this big pest introduced to his tank by getting rid of it before placing rock in his tank.
https://forums.saltwaterfish.com/forum/thread/386736/aiptasia