Action button

I am having a action button approve only for the department heads
The user will submit a record for more than one department head
Action button will appear for the corresponding department heads,if one department head approve the action button should not show to them,the remaining department heads should see the action button.
Can suggest some expression ??

You can build an expression based on the email address logged in. So for example I have a table called Custom Settings that ties the users email address with their name used throughout the app. Then I use
CONTAINS(SELECT(Custom Settings[Task Owner],([Current User]=USEREMAIL())),[Owner])

This will lookup the current users email address in my custom setting table and pass back their name and then I make sure that my user matches the current user. So in your example you would want to exclude the record if the current users name matched the manager filled out in a particular column and then not show the action button for that record.