A method of operating a system at an operation site, wherein the operation site is a wind turbine with a wind turbine blade having a surface, wherein the system comprises an unmanned robot, wherein the robot comprises a base, an arm extending from the base, the arm comprising a remote end configured for movement of the remote end relatively to the base, and a control unit for electronically controlling the operation of the at least one arm, and a spreader tool attached to the remote end of the arm and configured for spreading a viscous material on the surface of a curved section of the wind turbine blade, the spreader tool comprising a bendable spreader wing and a bending mechanism, that comprises an actuator for deforming the spreader wing into a variable curved structure and configured for adjusting the bending curve of the spreader wing to the curvature of the curved section, and wherein the method comprises locating the robot at the curved section, providing viscous material onto the curved section, orienting the spreader tool relatively to the curved section by the arm, adjusting the spreader wing to the curvature of the curved section by the actuator, and moving the spreader tool along the curved section by the arm, thereby dragging the viscous material along the curved section and spreading the viscous material on the curved section. an unmanned robot, wherein the robot comprises a base, an arm extending from the base, the arm comprising a remote end configured for movement of the remote end relatively to the base, and a control unit for electronically controlling the operation of the at least one arm, and a spreader tool attached to the remote end of the arm and configured for spreading a viscous material on the surface of a curved section of the wind turbine blade, the spreader tool comprising a bendable spreader wing and a bending mechanism, that comprises an actuator for deforming the spreader wing into a variable curved structure and configured for adjusting the bending curve of the spreader wing to the curvature of the curved section, and attached to the remote end of the arm and configured for spreading a viscous material on the surface of a curved section of the wind turbine blade, the spreader tool comprising a bendable spreader wing and a bending mechanism, that comprises an actuator for deforming the spreader wing into a variable curved structure and configured for adjusting the bending curve of the spreader wing to the curvature of the curved section, and wherein the method comprises locating the robot at the curved section, providing viscous material onto the curved section, orienting the spreader tool relatively to the curved section by the arm, adjusting the spreader wing to the curvature of the curved section by the actuator, and moving the spreader tool along the curved section by the arm, thereby dragging the viscous material along the curved section and spreading the viscous material on the curved section. locating the robot at the curved section, providing viscous material onto the curved section, orienting the spreader tool relatively to the curved section by the arm, adjusting the spreader wing to the curvature of the curved section by the actuator, and moving the spreader tool along the curved section by the arm, thereby dragging the viscous material along the curved section and spreading the viscous material on the curved section.