Depending on your siRNA you could use different approaches. If it is indeed an already processed, unique short interfering RNA, i.e. 21-25 nt, I think you could just map it to your reference genome and get a sense of how many off-targets you're facing. For that, I would use an aligner that can manage very short reads and multi-mapping reads, like Bowtie or BWA. If you want to avoid the command line, I think Ugene (free) and Geneious offer a graphical user interface and can align sequences to custom reference genomes.

On the other hand, if you're using a longer construct (~500bp hairpin, convergent promoters that generate a ~500bp double-stranded RNA) in order to generate your siRNA in vivo (and other different siRNA from the same longer sequence) you need to take that into account to predict off-targets. In that case, I would create a FASTA file with every potential siRNA that your template can generate. To do that, you can predict all 25-nt sequences or 25-mers in your template, if possible using a 1-nt sliding-window algorithm instead of just creating non-overlapping 25-mers. And then, map those sequences into your reference genome as above.

Hope this helps!

Ok, thanks!

You can take the help of the following computational tools.

1. BLAST

2. Targetscan

3. RNA22

4. Off spotter

5. CRISPR ERA

For more details please check

https://www.dlcompbiobiotech.com/2023/02/predicting-sirna-off-targets.html