Davinci Resolve: How to flip horizontal a short scene (visually flip every frame, without reversing play)
First, cut the longer clip into 3, to separate the reversed part from the rest of the clip. Then bring the clip into fusion, link the input to a transform node, then to the output. The transform node can flip horizontally on the right hand side panel options for it.

A shortcut to do this quicker is you can do it in the edit page also, by just selecting the clip and using the 'transform' attributes on the right hand side.