Handlebars will not fold. If the handlebars are bent the black slide will not lift up. Check them from the side and look for the bend. If it is above the slide the bars can be straightened. If the black slide is bent they will need to be replaced.
Handlebars are loose.
The mosquito handlebars are held in place with a wedge assembly. The fork is held in place by a silver washer and a gold lockwasher. If the t-bar seems loose in the fork or turns without the wheel the wedge must be tightened. Fold the handlebars and tap out the nylon plug. Align the wedge and tighten it with a 6mm allen wrench.