I pressed the button that grants the administration and an image appeared that an email will be sent to that person confirming the administration, but now I don’t want him to be in the administration anymore, how can I cancel this?
you should just be able to revoke the admin same way. can’t stop the email at this point but you can revoke admin status in the user profile admin.
Before that person gets an email, one is sent to you. Did you click the link in that email? If so, you should be able to just revoke their admin status, if not, you don’t need to worry.