How do I populate the cleanup_old_archives function and cleanup_old_disk_backup function?

[Clara Tang Ga Yi]

I am currently backing up using rsync method. I have set the $KEEP_BACKUPS to =30 however, I can see that more than 30 backups are getting retained and it is taking up my disk space. 

I have evaluated the .sh files and realised that the cleanup_old_archives function only has no_op instruction within.

How can I write the function such that it only keeps my specified number of backups I want.

Thanks