Work as an R&D trouble shooter and you have to speak to everybody that has done a bit of the project.
Make notes and draw diagrams, then have a coffee and think about what you have and what it should be.
Chat to few team members and hopefully see the solution to get to the next step.
After managing this for a couple of other projects, return to the ones that are still outstanding and look at them for the solution.
There is always something you don’t see the first or second time around, but the third or fourth time it stares at you.
SPRINT how to SOLVE BIG PROBLEMS AND TEST NEW IDEAS IN JUST FIVE DAYS by Jake Knapp with John Zeratsky & Braden Kowitz
If you buy the book new, there are extras that are worth having and using.