...and you generally want to add any fuel system cleaners to the tank just prior to the engine oil change.
There's usually no point in using the fuel system cleaners on a regular basis, the primary result will be a lighter wallet. The cleaner mfr's of course want you to shell out every 3kmi so they make more money, but that won't make a clean system any cleaner.
This assumes you only use Top Tier fuel, not cheap stuff. If using bargain fuel, use cleaner once, then switch to Top Tier.
https://www.toptiergas.com/