Does anyone know how to make this wok for Automatic Fire instead of Single Shot?

I'm not entirely sure what system you have set up, but it's pretty easy to do. Just use a while loop to make yourself keep firing.

local fire = false

mouse.Button1Down:connect(function()
    fire = true
end)

mouse.Button1Up:connect(function()
    fire = false
end)

while fire do
    wait(0.1)
    fire()
end

Of course this assumes that you have mouse and fire() defined somewhere.

To use your own code, OP, you're going to have to connect both the KeyDown and KeyUp events:

if (key == "f") then --[[in KeyDown]]
        if (not isFiring) and (not cloakActive.Value) and (not shieldActive.Value) and (speed.Value < fireSpeed) then
            isFiring = true

        while isFiring do
             fire()
              wait(weaponsCooldown)
        end
        end
    end

if (key == "f") then --[[in KeyUp]]
        if (not isFiring) and (not cloakActive.Value) and (not shieldActive.Value) and (speed.Value < fireSpeed) then
            isFiring = false
        end
    end

This requires isFiring to be defined outside of either event, however, so that the same variable is accessible to both.