Update index.md

docs/background/index.md

@@ -9,4 +9,4 @@ UK-TRE aims to encourage open collaborations and sharing of innovative ideas to
 Anyone can join our mailing list and attend our meetings, you do not need to provide any information other than your email address.
 
 :Mailing list: https://www.jiscmail.ac.uk/cgi-bin/wa-jisc.exe?SUBED1=UK-TRE-COMM&A=1
-:Slack channel: https://ukrse.slack.com/archives/C045ETUPPD0
+:Slack channel: https://join.slack.com/t/uktrecommunity/shared_invite/zt-2gep86apc-QMLyIdrC2oIIsxTRzLxUqA