You can close the account from either your mobile browser or web, however, this is currently not offered on the Gemini app.
First, you will need to have your account balance at $0. If you have any pending ACH transfers you will need to wait for those to clear after 5 business days to initiate a withdrawal, which you can do here: Transfer Page.
Once you have received your funds, please navigate to the Profile Setting's Page and follow the below steps:
Click on the hyperlink labeled "Close your Gemini account" at the bottom of the page under ACCOUNT CLOSURE.
To complete the account closure type in all caps "CLOSE"
If you would ever like to reopen your account, please email us back with the request and we can provide the steps to getting you trading again!