Finding square root of polynomial in extension field (Number field sieve)

Question

I was reading this paper, on page number 29, 2nd paragraph it is written that "take the coefficients of $ \gamma $ modulo q and applying an algorithm for taking square roots in the finite field Z[ $ \alpha $ ]/Q (see [19; 16, Section 4.6.2, Exercise 15]), we find an element $ \delta_{0} $ (mod Q) such that $ \delta_{0}^{2}\gamma $ = l mod Q". I cannot understand how we can find this $ \delta_{0} $.