There were many things that were tried. At first it was mostly inspections, evaluating the Blow Out Preventor (BOP), and trying to integrate our tools into it in order to perform valve operations in hope to choke the flow and kill the well. The operations were called "choke & kill."
Initially, the biggest endeavor was using a manifold on the seafloor to perform a "junk shot," which was basically a bunch of junk (golf balls, pieces of rubber tire, etc) that we're to be pumped into it in order to stop the leak long enough to find a more permanent fix. We used a 24" carbon circular saw blade attached to a subsea thruster (used to fly the ROVs). This is what we called a "Super-grinder." I cut the "choke" line and the "kill" line with the Super-Grinder via the ROVs Schilling Titan 4 (T4) robotic arm and we used the robo-arms to clamp a new line going back to the manifold. It didn't work as we'd hoped. Those choke and kill lines were flexible tubing, about 12-24" in diameter and took a few days to cut, as it was a tight spot and some of it had to be done blindly and/or using another ROVs video feed to see the other side while working backwards it seemed. Someone else was piloting while I was cutting and we swapped here and there.
Anyway, weeks later we developed a "diamond wire" cutting tool and lowered it subsea from our construction vessel. We got it into place with dual ROV ops and basically cut the top off of the BOP like it was a bandsaw. We placed a mini-BOP (developed in a quick-fast-hurry and began locking it down to the throat. We called this "putting on the wedding ring." The top of the mini-BOP was open to vent via four big needle valves. We did this while in the massive oil plume with zero visibility.
When the mini-BOP was locked onto the throat, we closed one needle valve at a time in a star pattern fashion. We did one, waited 15-30 minutes. We did the second, waited 15-30 minutes. We did the third, waited 15-30 minutes. We set on the 4th needle valve... put the manipulator jaw on the handle, and we began slowly... slowly spinning it for what seemed like 20 minutes while taking visuals of the entire contraption to ensure that back pressure didn't mess something else up and blow out. It was one of the most intense, fingers-crossed kinda moments of my life, white-knuckled while my friend/supervisor turned the final valve. The plume coming through that final, small vent just slowly stopped trickling through and that was that.
We spent 4-6 weeks observing the site, and communicating with gyroscopes (fun fact: they looked like jetpacks)and whatnot on the seafloor and eventually they broke it all down and put a final cap. The cap we put on can be seen online. It was a "In memory of" pressure cap with 11 stars on it. The final photo that I saw when I was offsite was crystal blue water and a solitary cap, like nothing was ever there, which is really fucking funny because it's like 7,000+ feet down and it's not blue down there, even with LED lights on the site.
Then we spent 4+ months via the moratorium starving for work, sitting at home after cleanup efforts at the site. I was lucky to be on the team and have those 3-4 months worth of work at the Macando site. That's it, my claim to fame. I was lucky enough to be part of a team that had a skillset strong enough to attempt all of that and do it successfully.