Full disclosure, I'm in a federal department that has been pushing for more open source for a while.
This is a great move by the White House. While there are a lot of groups that are trying to push for more openness and release of software, it can often be challenging. A lot of federal groups have been taught over the years to be very risk averse, and open software is viewed by them to be risk. Probably one of the most common concerns is, "What happens if someone takes and misuses our software?" In a highly risk-averse federal environment, these can be challenging arguments to fight against.
If you like and support this kind of thing, one big thing you can do is to contribute and supply feedback. We frequently have to go to our superiors and justify what we are doing with regards to open source. We say things like, "this repository had X pull requests from non-federal contributors". Or, "We got Y comments and questions from non-federal users of our projects".
It could be as simple as an email saying "Hey thanks, I found this useful", to a full-on pull request fixing an issue or with a new feature request. The more fodder we have to say "open source increases engagement and creates positive feedback" the more you will see this kind of thing happening.