How to tighten the handle of the dishwasher model #ZBD688

Depends on the brand and type of handle. I'll give you a few general ideas. The first easy one is to look under both ends of the handle for small set screws. If you see them, a small allen wrench should tighten the set screws and the handle. The next type requires the removal of either the inner door panel or outer panel. Some dishwashers will have screws along the inner edge of the door panel. you remove the screws and either the inner panel will come loose or the outer panel will come off (depends on make and model) Once the door is apart you should be able to see the handle screws to tighten. Some doors also have a screw in both bottom corners facing upward that may need removed . Best I can do at this time.

This model comes with two types of doors. One with a single panel with integrated control on top or a two part door with control unit in front. The handle varies.

If you have a single door panel with handle bar across from right to left then you need to carefully unscrew the back panel screws and free up the front panel. the handle is screwed to the front panel from inside. Once you tighten carefully put the back door panel in and tighten. Take photos along the way to make sure you get back where you started. Also unplug dishwasher before working on it.

If you have a two part door with front control then handle and access to it is different. See diagram on this website for blow up of the panel and location of handle (part 713).

ESCUTCHEON DOOR ASSEMBLY Diagram Parts List for Model GLD5868V15SS GE...

You can magnify the image or take a full screen view for clarity.

Open the door and loosen the self threading screws around the sides of the inner door panel. Once this has been achieved lift the inner panel up so that you can access the door handle screws. Tighten these fasteners and reassemble the door panel.

Remove front panel then you can access the handle screws. Open the door and remove the 'torx' screws surrounding the perimeter of the door.

Here are some manuals, maybe they will help, I haven't personally down what you are asking about, but maybe one of the manuals has an exploded view.

Thanks.
ZBD6880 GE Monogram Dishwasher
ZBD6880 GE Monogram Dishwasher Owners Manual
ZBD6880N00SS GE Monogram Dishwasher Owners Manual
ZBD6880 GE Monogram Dishwasher Owner's Manual
ZBD6880K00SS GE Monogram Dishwasher Owner's Manual
ZBD6880K03SS GE Monogram Dishwasher Owner's Manual
ZBD6880K15SS GE Monogram Dishwasher Owner's Manual
ZBD6880N00SS GE Built-In Dishwasher Install Instructions
ZBD6880N20SS GE Built-In Dishwasher Install Instructions
ZBD6880 GE Monogram Dishwasher Manual

Ok you need to use plastic or rubber washers against the glass so it doesn't break. To stop the handle comming loose again you need to put "Lock Tight" on the screw threads then tighten carefully only untill the handle isn't loose. You can get this from any good hardware store. cheers

Please give feedback

Take the inside panel off.  The 2 screws near the latch only need to be loosened.  Once the handle is off, you will find an allen bolt inside the shaft of the handle support.  Tighten and you are done.

Handle needs to be replaced part# 154537303 (blk). Un plug unit, take 4 screws from behind blk control panel out. Panel will fold down, remove two torx head screws from door latch, replace with new one and put it back together and your done.

THIS IS THE SOLUTION!
I was having the same problem with my Monogram dishwasher and oven.  Here's what to do.  You must fully remove the handle from the appliance.  Down the barrel of the standoff is a hex screw that, when tightened with an allen wrench, will draw the standoff tight to the handle again.  There is no need to remove the end caps. 

There should be a slot for an allen rench on the under side of the handle that will tighten the handle up.