On your iPhone, iPad, or iPod touch with iOS 10.3 or later
Tap Settings > [your name] > Password & Security.
Tap Change Password.
Enter your current password or device passcode, then enter a new password and confirm the new password.
Tap Change or Change Password.
NEVER give ANYONE your password or other logon details (or bank pin number or a "one time payment" (OTP) number), even if the people who phone up say they are the police or your bank.
In fact ANYONE who phones you up out the blue be VERY wary of them.
(I know you may not have got phoned up by anyone but it is all just good advice)