i received an email saying you see unusual activity and that you locked my account. what shoul i do

This may be a Phishing email, sent out to obtain your information. Do not click on any links.

Check the Contents of the email. If there are any grammatical errors, or anything that doesn't look right, its likely a phishing attempt.

Try downloading or updating an app. If you don't get any errors, you are in the clear.

Change your password as a precaution. Settings > Tap on your name at the top > Passwords and Security > Change Password

https://support.apple.com/en-us/HT204759 < More information about phishing and how to avoid it.

Apple won't send you an email/text telling you your account is disabled/restricted  or will be disabled/restricted. You will find out the next time you try to log in somewhere.

Apple will always address you by your name or the name they have on file for you, not Dear Customer, Dear Client or by using your e-mail address.  The e-mail will be from @apple.com or @iTunes.com. E-mail addresses can be spoofed. You can go to Mail/View/Message/Show all Headers to see more. Apple e-mails will never contain an attachment. Apple will never request personal information by email such as Social Security numbers, your Mother’s maiden name or full credit card numbers .

The only exception to the above I have noticed is if you order something from the Apple Store (apple.com), your receipt will be addressed to Dear Apple Customer. That is a receipt for a purchase you initiated.

Identifying legitimate emails from the iTunes Store

Send the e-mail to Apple as an attachment to a new e-mail before deleting it. You can forward as an attachment by going to Mail/Message/Forward as attachment. You won’t receive a response.

reportphishing@apple.com