I lost mine so I modelled one up. It's designed to slightly bend and then hook itself under the keycap. You only need to hook one end and the friction alone on the other side will give it a secure enough of a grip to remove the keycap. 

I haven't had any issues on the mechanical keyboards I own, but if there are fitting issues, please scale it appropriately as each manufacturer have different keycap designs. 

I've included the STEP and F3D files available for download. Feel free to adjust it to your own needs. 

NOTE: 

• PLEASE MAKE SURE THE SEAM IS NOT ON THE PORTION THAT BENDS, ELSE IT WILL SNAP. IF YOU DON'T KNOW HOW TO ADJUST THE SEAMS, USE THE 3MF PROVIDED AS REFERENCE. 
• PLA IS OK TO USE, BUT WILL GENERALLY FAIL FROM FATIGUE. I RECOMMEND USING PETG, ABS, NYLON OR ASA. DO NOT USE FIBRE FILAMENTS BECAUSE YOU WILL GET THEM IN YOUR SKIN.