After you tell your manager, you won't be in control of what happens next. Consider whether or not you should just keep this to yourself and treat this as a fun learning experience. Perhaps you can gauge their potential reaction by asking, hypothetically, whether or not they think working on automation might be a good idea.
I've done something like this before, but with the knowledge of the other people on the team, because we didn't like the manual work we were doing and felt that it was taking time away from other things we needed to do. Hopefully that is the case for your colleagues, or this will not be well received.