keep/stretch a frame for more time during a video

How can I do this with QuickTime (sorry I don't know the exact nomenclature): - I have a saved recording of my screen (i.e. the question is about/for mov files) - I want to replace the video (only!!!; keep the audio part intact) from a certain moment to another moment with a static image OR I want to stretch the time an image/frame is displayed in the video for a longer time. Is this possible with the default apps from MacOS Sonoma 14.5? And if so, how? (I'm new to MacOS ecosystem, so please give me a step-by-step recipe.)