Your ICC is your sailing license that is accepted everywhere so it is this that you should renew.
The renewal documents can be downloaded from the RYA.org.uk site. At the time of writing, this is the page where you can get the renewal document: https://www.rya.org.uk/knowledge/abroad/icc#link3
If you are wanting to renew your SLC go here: https://support.nauticed.org/a/solutions/articles/44002149749