How to update the boundary conditions of one case according to fields of another case
 

As shown in the figure, the external grid is coarse and the internal grid is fine. I need to update the boundary conditions of the fine mesh periodically every few seconds according to the information of the internal field of the coarse mesh. The solution I know now is to use the mapFields command to map the internal field information of the coarse mesh to fine, but this command can only be updated once. My question is how to call the function corresponding to the mapFields command in the existing pimpleFoam solver to meet periodic updates. Or is there any other plan? I would be grateful if you could give me some help.