How to add a 1 mm deep slot in this inside offset around the whole piece

Hello from Spain. Very much a beginner with Oshape and CAD.

I need to add a round slot 1 mm deep/ 1 mm wide, around the whole perimeter of this piece (on the yellow line).

I've tried drawing the offset line inwards, and then apply SLOT, but I can't get it to work properly!

Thank you!

Screen Shot 2025-08-24 at 10.58.58.png

Answers