Just turn the power off and physically push until both linear modules hit the endstops. Remove the X-axis first if you think it’s necessary or useful to do so. It isn’t unusual for the modules to become misaligned on the larger machines that have two per axis. You might want to run a test afterwards to make sure both modules are still working correctly (just jog it a bit with the X-axis detached and make sure both modules are moving).
If you have problems of misalignment it could be necessary to tram the x axis on metal cans or something similar and loosening the screws before fixing it again to avoid tension on the modules and construction.