You have two processes to change your Club name, which are: 

1- Click on your avatar, and you will have access to your manager info, where you can change the name of your Club and much other info.  

- Click the pencil icon in front of your club name to edit it. 

2- The second process is as follows:

- Click on CLUB on the main interface, then on PREVIEW,

- By tapping on the pencil icon you can change the name of your Club.

Changing your club name for the first rime is free. Then it will cost 1 Coins.