Rotating Frames in iMovie

Hello and happy Saturday to all,
And the problem is... someone sent me some videos that were taken with their iPhone that needed rotating. Not a problem for the entire clip using iMovie, (and which I really need to buckle down and learn properly) but the person taking the video must have changed the orientation (toggled the iPhone) while filming and therefore half the movie is portrait and the other half is landscape. Without having to actually buy (things are tough) a plug-in for iMovie, is there anyway that anyone knows of to rotate the single frames that so that I can match up the two different orientations?
Thank you very very much.

Split the clip at the point where the rotation changes and then rotate the portion that needs it.

Thank you, I tried that and assuming I did it correctly, (maybe not...) I selected the frames that needed rotating in the "event" panel but the moment I hit the crop, rotate and ken burns, it automatically selected the entire clip, thus, therefore and forthwith successfully defeating the whole purpose of only rotating certain frames.

You can only split a clip when it's in a Project, not in the Events Library. With it in a Project, move the playhead(the red vertical line) to where you want the split, then Right(or ctrl) click, then choose Split Clip from the menu.