How do acoustic peaks in the CMB appear if the universe is positively curved?

They would appear magnified, appearing larger than expected

The observed angular size of the acoustic peaks—the hot and cold spots originating from density fluctuations in the early universe—is highly sensitive to the intervening geometry between the source (the CMB) and the observer. If the universe has positive curvature (a closed geometry), the space through which the photons travel acts like a converging lens. This effect magnifies the apparent size of the distant features on the sky map. Therefore, if the universe were positively curved, these known physical features would appear larger than they would in a perfectly flat space. Conversely, if the universe were negatively curved (open), the geometry would cause divergence, making the spots appear smaller than expected. The fact that the CMB spots match the theoretical size predicted for a flat geometry is powerful evidence supporting the $\Omega=1$ model.