You can simply push directly on the derailleur lower knuckle.

But really, set up your stops, then connect the cable and adjust tension. You shouldn't need to monkey with the stops after they are set up, except for tiny changes that can be made under cable tension.

Sometimes people think derailleur adjustments are more complicated than they actually are. The stops are a very basic adjustment and don't require tinkering or readjustment, while tension is just more or less. If the bike isn't shifting right, it is unlikely that it is because of some fine tuning issue.