Read the manual you'll have received with the fridge.
Page 12, reference to item 10
Manual available from this page:
https://www.bosch-home.co.uk/product-list/KUR15A50GB#/Tabs=section-technicalspecs/Togglebox=manuals/
Personally I find the old school plastic coated spring, the stuff that folk use to hang net curtains, is really useful for clearing out the drainage hole.
Dghj
December 2023