Surface corrugations in graphene negatively effect the unique and useful properties of graphene. In order to exploit the special properties of graphene, it is therefore important to understand the phenomenon of wrinkling. In this study, strain engineering was applied to study the flattening of wrinkles in a suspended graphene membrane. Initially, a MEMS device was used for inducing strain in a suspended membrane. Transfer of graphene onto the MEMS device was challenging and in this study not successful. Suspended graphene drums with an electrostatic backgate were used as an alternative system for strain engineering. A stress-strain curve was calculated from the drum deflection measurements as a function of backgate voltage. The stress-strain curve exhibits a non-linear regime that is due to wrinkle flattening and a linear regime that is due to membrane stretching. The Young’s modulus of the membrane is determined using three different methods. An analytical model for the stress-strain curve of a wrinkled membrane proposed in [1] is fitted to the experimental data. The good agreement between the model and the data validates the model and provides insight into the parameters that govern the behavior of the membrane. Wrinkles were visualized individually and were clearly decreasing in size with increasing backgate voltage. Also the surface correlation length was shown to increase with backgate voltage, indicating flattening of wrinkles.