I looks like you got some good advice already [@mention:491213757235914012]. I would add that addressing this kind of issues, which involve a lot of small behavior shifts rather than one change, is exactly what a good coach is useful for. So if you have a coach ask them to help -- especially during tactical meetings. If you don't, well something to consider
Aside from that, the first thing I would do is try to understand why people aren't doing it. And it might be different reasons for different people. Based on that the best actions will be different. But one possible (and frequent) reason is that people don't have a solid individual trusted system, like Getting Things Done (GTD), to keep track of the things they've agreed to do. If it's the case. I would suggest investing in that area.
As a tip, if you need to remind someone of doing something regularly, then it's really inefficient and a drag on your own work time. You could then ask the person to define a personal process for making sure that they catch it and do it themselves, without you having to "poke" them. After all if you're doing that, that's because they're dropping something they are already accountable for. Concretely, you can ask them to capture a project (e.g. "Process in place to consistently add name on blog post spreadsheet every week" or whatever). Once the project is captured, you can ask for updates on that, and offer help (or even defining a role, e.g. "Personal Organization Coach") for how to do that best. Again, that's where a good individual trusted system comes into play.
I'd also use checklists during tactical meetings to get visiblity on whether people have done something — it systematizes the reporting of whether they have completed an action or not, so it's not "you" poking them, it's just one of their checklist items. And if they say "no check" you can ask clarifying questions ("why didn't you do it? what got in the way?")
Finally, I'll emphasize what others have said: poking people because you're the founder is not a good reason, but poking because you are the Lead Link, or any other role that directly cares, is perfectly appropriate in Holacracy!
Hope that helps