How to implement the federated XGBoost by getting the Gi and Hi values from nodes, saving them in a file, aggregate them and pass them to XGBoost?

Question

I need to get some results for federated XGBoost but I just want to simply get the hi and gi from each node and same them, then aggregate it and pass the new Hi and Gi to the nodes to use it and test the XGBoost with new parameters. I could get the g and h values but don't know how to aggregate them and pass the new values to the XGBoost to use it for testing. I would appreciate if anyone can help me. Thanks in advance