The original glue was very likely hide glue, which may be purchase from Stew-Mac
. Hide glue
is easily "undone" using heat and/or steam, should one make a mistake. These days, many use Titebond
aliphatic resin glue (Original only, not
type II). It's a little more difficult to separate for repairs, but is good stuff.
For a bridge reglue, you will need to remove all the old glue from both guitar and bridge, as well as make sure these still make good contact over the entire gluing surface. Make sure the top and bridge are not warped or bowed, and all internal braces are still intact. Also, given the bridge "fell" off, it is a good idea to check for other glue deterioration.
If this guitar is worth something (seems likely), you may wish to have a luthier do the repair.
Good luck -- Greg