You have a couple of options…one will be to allow Glowforge to repair it for you. Since it’s now out of warranty, they will suggest that you ship it to the technicians to allow them to repair it, and it will probably run a few hundred dollars. (You’ll be charged for round trip shipping, the cost of replacement of the glass and recalibration to ensure that the machine works the way it was intended to.)
Or you can attempt to repair it yourself, there are discussions in the Beyond the Manual section that other people have had varying degrees of success with. One linked below:
You might do a search in the Beyond the Manual section to see if there are any others, just search for “glass fix”.