Where to find the necessary js functions in Bitrix?

Question

JavaScript

Greetings. There is Bitrix24 (it is almost the same as Bitrix CRM). There is a task to make a small change in the JS code. There are no problems with the code. There are problems with how to find it and make changes so that everything is not overwritten during the update. Given:
OnBeforeBuildSceletonCCalendarSceleton::Build
OnAfterBuildSceletonCCalendarSceleton::Build
In these events, you need to override the plug-in js functions that form the appearance.
Connoisseurs of Bitrix, tell me how to do it right.
Thank you.