How do i de obfuscate a lua code

i have a obfuscated lua code and i want to de obfuscate it. i did a bit now im stuck with

math.randomseed(9891861);
RunString(("aab1....

_f = _G.RunString
RunString = function(mom)
print(mom)
_f(mom)
end

Start script
(https://pastebin.com/RKjjVW53)