If you're looking to downscale footage (as opposed to upscaling it), you'll need to choose 'Bicubic Interpolation' under Filters > Scaler once you've entered the Process Tool.
After you've chosen Bicubic Interpolation, you'll have to choose the Custom option and enter the resolution you want to downscale to.
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P.S. If you run into difficulties or have any questions, please reach out to us here or at help@pixop.com — happy to help 🤓