How to make my object whole?

Hi, Creators-
Finally jumped in to Sketchup and really like its attributes but being a newbie i need some help please.
I am 3D modelling, in scale, a garage renovation into living space. But related to this topic I imported a double hung window but some of the elements while all connected did not reflect the actual or typical construction of a window. Deleted all entities except the two sashes and built a frame and details on them to reflect accuracy. Turns out the lower sash is a component and won’t attach to the rest of the model…the main model is a Group.
Tried right command selecting various, while the lower is selected but options won’t allow attaching to rest of the model.
ideas welcomed and appreciated!!
Isitdav