Your question is not quiet clear. What do you want to register? "Intervention" seems not to be the appropriate word for an experimental study. - The best way to make a scientific study known to the public is to publish its results as a scientific paper in a journal. Additionally, you may upload your data to ResearchGate. See https://explore.researchgate.net/display/support/How+to+add+research for instructions; click on "Add new" and then on "Data".
The WHO trials registry is for clinical trials, although it depends on your trial question; some studies have socioecological aspects to them but are still medical or clinical in nature.
You say you are conducting a social science RCT -- then you could consider registering with the AEA: https://www.socialscienceregistry.org/
Might be worth asking your trial supervisor for their recommendation.