Need step-by-step help on how to shred files in the Recycle bin
This isn't a function, specifically, that CCleaner includes.
What you could do would be enable Options > Settings > Secure Deletion and set it to the specified number of passes, then use the Health Check or Custom Clean (with Windows > System > Empty Recycle Bin enabled in the latter case). That will cause all data that's deleted in this process to use the Secure Deletion process, not just the Recycle Bin. Please note that this will make the cleaning take much, much longer than it would without Secure Deletion enabled.
You could alternately clean as normal (even just using Windows' Empty Recycle Bin command), then go to Tools > Drive Wiper and wipe the drive's free space. More information here: https://support.piriform.com/hc/en-us/articles/204043884
Please note that this is not recommended on solid-state drives, USB Flash drives, or anything else but a standard, conventional spinning hard drive because it may reduce the drive's lifespan and, more importantly, will be ineffective. More information here: https://support.piriform.com/hc/en-us/articles/360040276031