Convert Framerate WITHOUT interpolation

[YaBoyShredderson]

im using staxrip to convert some variable framerate footage from my phone to constant framerate prores to be edited, but i cant work out how to change the framerate without interpolation? all i want to do is convert the framerate without changing the runtime. if i convert using x264/5 and change the frame rate in those settings, it just speeds up/slows down the footage. with prores, there is no framerate setting, so i have to use avs. I click on framerate, click on convertFPS and then select what i want it to be, but it interpolates to that framerate, i realised when i read the readme in the files for staxrip. how do i get to change the framerate without interpolation? handbrake can do it, but not to prores.