The main goal of 6G is to realize the intelligent interconnection of everything, and Reconfigurable Intelligent Surface (RIS) and Unmanned Aerial Vehicle (UAV) communication technologies are expected to provide feasible solutions to achieve this goal. In order to solve the problem of interconnecting everything at 6G using these two technologies, we propose an airborne RIS-assisted relay-based communication scheme and mathematically model the system model, and since the problem is non-convex, the suboptimal solution of the optimization problem is obtained by using the semi-positive-definite relaxation algorithm (BCD) and the successive convex approximation algorithm (SCA). In order to maximize the average achievable rate, we co-optimize the user communication scheduling, RIS phase shift and UAV trajectory. We introduce a hybrid optimization approach that combines offline and online techniques, leveraging real-time channel information to enhance system performance. Simulation outcomes illustrate that this combined approach considerably exceeds the performance of the reference method regarding the mean achievable rate.