SourceTracker2 input files

Hi there! I'm trying to use sourcetracker2 for the first time and I have some doubts about how to start.
What I have is a fastq file generated from a metagenomic sequencing.
What I want to do is to understand where the microbiomes I've found with the taxonomic classification come from.
I thought Sourcetracker2 could be a possible tool to do that.
Since I need an OTU table and a mapping file with information about my sample and also the biome from known sources I have thought that I could download other fastq file (of samples with known origin such as skin, nose, soil, water, ...) from online databases, put them together with my fastQ and use QIIME (manifest protocol) to create the OTU table.
Is it the correct workflow I should follow?
If not, can you suggest something different?

thank you so much for your help!