To use the filter, run your search in PubMed and then copy and paste the text from the search. Add it to the last line of your search strategy.
If you are trying to locate prior systematic reviews: If you don't find anything when you use the SR filter, consider removing a concept from your search strategy, i.e. make it broader. In the search example to the right, combinations of concepts are used to identify potential SRs as well as clinical trials studies. The rationale for doing it like is that authors don't always describe in their titles or abstracts exactly what they've done so we have to sometimes broaden the search a bit to ensure nothing is missed.