Make sure the silicone gaskets are in the correct slots. If they slipped out during the removal process, use tweezers or something small enough to push them back in.
Lubricate the glass with little alcohol or water, then carefully slide them into their shell.
Twisting while you push may help.
Re-connect the stem and tighten the bottom accessory port.
Tip: The stem does not need to be threaded all the way tight. You could leave it snug for an easier removal next time.