For this kind of work, you should clone the server and run it in a test environment.
This must be changed:
ucr set locale/default=en_IN.UTF-8:UTF-8
Then rerun the join script:
univention-run-join-scripts --run-scripts --force 35univention-self-service-passwordreset-umc.inst
I guess you can change the locale back after that - not sure though. Nowadays you’d want all UTF-8 anyway.