I guess you used this: https://vismajorspeedruns.github.io/osu-font-converter-js/ If I have true so check the option "export as @2x", and you will have @2x files. Then create a copy of all images, remove the @2x to these copies, and resize these image to divide by 2 their height and width.
Else:
If the current files names have "@2x" files: reduce their size by 50%. Create a copy of all files you resized, remove the @2x to these copies, and resize these image to divide by 2 their height and width.
If they haven't the "@2x": add a "@2x" at the end of each files names. After, create a copy of all files you resized, remove the @2x to these copies, and resize these image to divide by 2 their height and width.