A question about tilt and turn windows

The window mechanism needs reset There is usually a spring or button ne'er the handle On the inside edge of the window Hold this spring back and turn the handle up To reset the mechanism

Looks as tho the mechanism is in two minds normally closing the window and putting pressure on the sash part to keep it closed is sufficient to make it work again ,sometimes there is a little spring on the sash near the handle you don't normally notice but with the window open this locks the movement of the handle pressing the spring or closing the window do's the same job , if still having problems consult an expert the window might need setting up physically if its old as they do drop , not an expensive job half hour to 3/4 shold ber sufficient

It sounds like the locking gear has slipped some teeth on the gearing I would of thought this is a little bit too complicated for a diy repair, someone within the window industry should be able to sort this out for you and as already stated not a big job.