Finding an asymptotically tight bound for a recurrence using the substitution method

Question

I need to find an asymptotically tight bound for $T(n) = T\left(\sqrt{n}\right) + \theta\left(\log\log n\right)$,

$T(4) = 1$.

I think the first step is to define $m =\log\log n$. What do I do now?

Thanks.