IKEA HÄLLVIKEN Sink - Drain eccentric set?

If drilling, then drill with a glass drill and then grind out.

I will try, thanks

According to the instructions (and that’s how I did it), use a screwdriver and a hammer, place it in the center and strike firmly. The opening has predetermined breaking points. Nothing went wrong.

Unfortunately, the instructions were not included and I can’t see any predetermined breaking point on this side. I will try it with a glass/tile drill.

Here you can download the manual:

Ikea.com/de/de/assembly_instructions/hallviken-einbauspule-becken-abtropf__AA-2054219-2_pub.pdf

See page 26.
I just checked my sink, there is a circular recess on the underside on both sides.

Here you can download the manual. I just checked my sink, there is a circular cutout on the underside on both sides.

I could have come up with the idea of the manual myself. I really didn't see any cutout, I looked quite closely because I expected there to be one. It would definitely be much easier. I'll have to check again tonight. Thanks for the help!