For example, if on the photo right half of the image is mirrored to the left - you making reference copy of the image, cropping one image from the left (leaving right half), mirroring it (in OBS it is named Transform > Flip Horizontal ), and placing it over the full image (so it covers only left half). Now you have two layers that look like "right half of the image is mirrored to the left".
Experiment a bit with required side cropping, flipping and placement.