Glass loose in top window

Hi hope you can help, we just moved in to our new (to us) house and the glass in one of the top windows rattles when it's windy, we didn't notice this when we looked around the 3 times we viewed the property before buying.

It is really annoying and we don't want to wedge it in case we break the double glazing glass, have you any idea what we need to do to fix it cheaply as we are a bit financially stretched with just moving and everything.

Thanks Jan.