Go to your device's Settings, scroll down and tap MailAccounts >Add Account.

Device Settings > Accounts & Passwords

Tap "Add Account"

Image of a grey lineSelect Exchange.

Choose Exchange

Image of a grey lineEnter your Microsoft 365 email address, password, and a description of your account. Tap Next.

Note: Your email address should be your Microsoft 365 business account or school account. Such as you@contoso.cn.