How to process the data with only one index ?

Hi,
I'm Hanwen. I saw the usage about sabre on website (https://astrobiomike.github.io/amplicon/demultiplexing). And it is mentioned in the end of this document that the data with one index can be demultiplexed. This is the key problem in my current analysis project and I don't know how to address it. Could you help me to do it? 