While there was very little to be done technically - we just needed to change a few settings at the point of public TLS termination - we still needed to announce the deprecation well in advance; coordinate with support teams to ensure that as many customer questions as possible would be answered; and remind, remind, remind, remind those end users. Much of the work we did for Bitbucket Cloud was later adapted for Atlassian as a whole.
Later follow-up work on this front helped Bitbucket implement TLSv1.3, once it became available.
Project link: https://bitbucket.org/blog/deprecating-tlsv1-tlsv1-1-2018-12-01