EOS R6 Mark II R6 R5C R5 Eye Cup Eyepiece, Extended Long Soft Eyecup Viewfinder for Canon EOS R6 Mark II R6 R5C R5 Mirrorless Cameras(Not for R5 Mark II), R5 R6 Soft Rubber Eyecup for Eyeglass Wearers

You can get a replacements on Amazon for around $20. It comes with a small screwdriver remove the 2 small screws the eyecup underside. Be careful as the will strip easily and once stripped it’s a REAL job to get them out. You’ll need to apply a lot of pressure to ensure the bit stays seated firmly in the very tiny head of the screw and turn slowly until the screw starts turning, then let off the pressure and remove. I’ve changed out stock eyecups on both my R5 and R6ii with models that have an extended cup to help block light. https://a.co/d/07XegRur