This is how I remove and replace the clip that holds the rear hub sprockets on a Brompton 2 speed. The only tools required are a pair of hands and a (very)thin narrow blade screwdriver, plus some care to prevent stabbing one's fingers with the latter, or letting the spring to, well, spring, into the eyes (not necessarily of the mechanic...)
note where it has been lifted in realation to the spring gap position
now pay attention that it might spring back...
Put it back in place: the spring gap is inserted in the groove under a tooth of the hub spline
and levered the opposite side holding it down so that it does not jump off the groove
thanks to the friends from the BromptonTalk list, that's where I learnt how to put the spring back!