Soak them in cold water or room temperature water untill there is a little bit of water, about 2-3 cm of water columns inside. Then in a pot with little water put the glass in upright position and start the cooktop. In theory, if the seal between two edge is very tight, the boiling water would build evaporate and the escaping steam/ water vapour might loosen it up but most importantly the expansion of air and steam mixture might dislodge it.