I have recently joined an organization that is experiencing challenges in predicting the delivery from its dev team, and I want to help them team back on track. So my manager asked me to report with a plan:
1. What is the approach I need to take?
2. What are the tools or techniques that I have to use since they already started practicing Scrum?
3. What do I need to focus on for the next few sprints?
In my opinion, you should have the team discuss and do a root-cause analysis of the issue in the retrospective. It can be pretty much everything, i.e. a lack of availability of the Product Owner leading to uncertainty during the Sprint, a high level of technical debt, a lack of knowledge or availability in the development team, or many other reasons...
The tools, techniques or focus will depend on the root causes.