$\begin{array}{l}\text{ But-2-en-1-ol }\stackrel{\mathrm{X}}{⟶}\text{ But-2-enal; }\\ \text{ But-2-enal }\stackrel{\mathrm{Y}}{⟶}\text{ But-2-en-1-ol }\end{array}$
X,Y respectively

PCC converts alcohols to aldehydes, as it is partial oxidizing agent. LiAlH₄ converts aldehydes to alcohols, as it is strong reducing agent and cannot reduce double bond.