Micron-scale mobile robots are being widely used in bioengineering applications, such as in a lab-on-a-chip (LOC) device, due to their capabilities of manipulation, sensing and transportation. Shear rate dependency of rheological properties of a non-Newtonian fluid enables swimming using geometrically reciprocal motion for a microswimmer. Therefore, it is not mandatory to use propulsive mechanisms that are slender in nature such as artificial flagella or cilia to generate non-reciprocal motion. We propose a design approach based on numerical simulations to select a suitable artificial appendage geometry to be used as a propulsion mechanism for a mobile microrobot. Here, the artificial appendage is considered to undergo rowing motion to generate propulsion. The fluid-structure interaction is computed numerically and three criteria are considered for the selection. In this study, a rectangular and a circular geometry are compared highlighting the proposed approach. The circular geometry showed better capability in terms of propulsion force generation, making it more suitable as a propulsion mechanism.