If you're already logged in to your Zoho account from your default mobile browser, the Zoho Mail mobile app may automatically add that same account. This can cause repeated additions of the same account in the app due to the active web session. To resolve this:
Open your default mobile browser.
Go to accounts.zoho.com.
From Sessions > Active Sessions, hover over the mobile device and click Terminate.
Go to the Zoho Mail mobile app.
Tap the Hamburger icon in the top-left corner of the app.
Tap the Settings icon.
Tap the + Add Account option.
On the sign-in page, enter your Zoho Mail credentials and sign in.