Famous German overclocker der8auer delidded the AMD Ryzen 5 2600 processor and uploaded a YouTube video that describes the whole process. The conclusion is that it's not really worth it to delid a Ryzen processor because there's too little to be gained. These processors feature indium solder underneath the internal heatspreader (IHS), which makes delidding not only harder but also less worthwhile.
der8auer replaced the indium solder with Thermal Grizzly liquid metal paste and ran benchmarks with the AMD Ryzen 5 2600 overclocked to 4100MHz at 1.35V. The conclusion is that the delidding process resulted in a temperature drop from 64°C to 60°C. So unlike with Intel CPUs, it's not really worth the risk because AMD is already using high-quality stuff.