We further investigate the 3d gauged linear sigma model (GLSM)/ quantum K-theory correspondence for partial flag manifolds $\textit{X}$ ≡ Fl( ; $\textit{n}$). This is a 3d uplift of the 2d GLSM/quantum cohomology correspondence with the 3d theory compactified on $$ {\mathbb{R}}^2\times {S}_{\beta}^1 $$ . Recently, a set of half-BPS line operators, called Schubert line defects, were constructed that correspond to the Schubert classes in the K-theory ring of $\textit{X}$. Utilizing algebro-geometric algorithms, we compute 2-point and 3-point correlation functions of these line operators in the 3d A-model regime of the theory. These are interpreted as genus-0 K-theoretic Gromov-Witten invariants, and they produce the K-theoretic Littlewood-Richardson coefficients of the quantum K-theory ring of $\textit{X}$. We show how this works explicitly in examples, going beyond the existing results in the literature. Taking the small $\textit{β}$ limit, we apply these techniques to the resulting 2d GLSM. We explicitly compute the quantum cohomology ring relations of $\textit{X}$ for some cases and match with existing results in the literature in examples.