Check if a string is not part of an array?

Well what your doing is comparing a string to a table, if you want to check if a string is inside a table we will have to go through each one and check individually

local t = {"PrimaryPart", "Head", "HumanoidRootPart"}

local checkname="string"

local isin=false
for _,v in pairs(t) do
    if v==checkname then
        isin=true
    end
end
if isin==true then
    print('run')
end

Here I set up a variable and then made a for loop to go through each string in the table, if the current string is the same as the string we are checking it makes a bool variable true.