But he's right. He can't run on the pitch and kick the ball himself.
The job of a football manager in a matchday context is to ensure that players have chances and stop chances against them. That's all they can really do. I think it was Arrigo Sacchi who said that the manager during a match is responsible for about 5% of the performance either way because they can't influence events too much, only change shapes and strategies in order to create or stop the creation of chances.
This is a professional elite level and not youth football. In youth football you need to work on shooting, on heading, on the basic skills of the game like that. Doing that to a professional player would almost be insulting - like you been a 15 year veteran in your job and been sent back to primary school to learn how to count or something. They already know and have the fundamentals of the game down.
Sergio Aguero doesn't need shooting training. He's scored over 300 goals at a professional standard over a 14 year career in three countries and representing his nation in World Cups. He knows how to shoot. I think you'd be right in suggesting that he's taking different types of shots now so there would be an adjustment period where his brain needs to develop as quick as his feet, but there's no way you can really coach this outside of putting him in matches.
If you're creating lots of decent quality chances over and above the chances you give away then the manager is doing his job. That's really all tactics can achieve. The rest is the mental part of the game which can only be dealt with by the player themselves, obviously with the help of the club staff if needed. But there's no training drill to improve this situation, it's on Sergio to break through this barrier on his own and I for one back him to do so.