Deleting an API Key and deleting your account are irreversible decisions. Once you've confirmed you want to delete an API Key or your account you won't be able to recover them again.
Deleting an API Key
Open the account manager menu in the bottom-left corner
Press on the 3 dots next to the account you want to delete
Press "Delete"
On the pop-up press
Deleting your account
Open the account manager menu in the bottom-left corner
Press on the settings icon
Scroll down to "Delete my account" and press
On the pop-up you'll be asked to enter the text DELETE-ACCOUNT to confirm you want to delete the account