If the hood is still closed, you may need to pull the latch harder. If the hood does not pop open after multiple attempts, the hood release cable may be broken. Ask a mechanic who is familiar with Mini Coopers to look at it for you.
There is also a metal loop attached to the hood near the latch, which is not the latch. However, the latch is located just to the left of the metal loop. The metal loops help keep the hood in place when it is closed.
Have a mechanic who is familiar with Mini Coopers troubleshoot your hood release latch.
The lower cable opens the right side of the hood, and the upper cable opens the left side of the hood.