Duet question


I have a video on my tiktok with a cat. My wife wants to duet it with
a video that she has on her phone. I have been watching videos of
how to duet but they just show filming a video along side of the other
video. I do not see an option to upload a video to put side by side
with the other video. Is this possible? Thanks.

System Configuration: Windows / Edge 94.0.992.50