first unscrew all screws from both sides of the glasses

Next insert the old lense (or new one depending on how damage old one was)

Now glue the two broken pieces together and hold together for about 30 seconds to 1 minute

(Optional) place glasses in between a vice and secure to make glasses fitted nice and tug. Keep glasses in vice until fully dried

once glue is fully dried carefully place screws back into place and tighten them all the way