Yes, providing you did not delete the message thread.
Ipen the message. Click reply. When the blocked screen comes to tell you you cannot message the user, you will see 3 grey tabs. The right most one with 3 dashes and the word menu will have a drop down that says report user.
Hope that helps!
On Mobile:
Go to the user's profile, tap the menu icon (top-right), and select Report User.
On Laptop/PC:
Go to the user's profile, click the menu icon (left-hand side), and select Report User.
