First, you should read this issues, then you would got a overview of it. and should able to use this docker image
Now, let me show you how to modify and run it easily.
cd /root/FTS/libssh-2017-1272
vim build.sh
cd .. && ./libssh-2017-1272/build.sh
./libssh-2017-1272-fsanitize_fuzzer
Best wish to you, good luck. (may be you should modify libssh_server_fuzzer.cc
by yourself.)