We assume that you can build Skia. Many fuzzes only reproduce when building with ASAN or MSAN; see those instructions for more details.
All that is needed to reproduce a fuzz downloaded from ClusterFuzz, oss-fuzz or fuzzer.skia.org is to run something like:
out/ASAN/fuzz -b /path/to/downloaded/testcase
The fuzz binary will try its best to guess what the type/name should be based on the name of the testcase. Manually providing type and name is also supported, like:
out/ASAN/fuzz -t filter_fuzz -b /path/to/downloaded/testcase out/ASAN/fuzz -t api -n RasterN32Canvas -b /path/to/downloaded/testcase
To enumerate all supported types and names, run the following:
out/ASAN/fuzz --help # will list all types out/ASAN/fuzz -t api # will list all names