Constraints issue

Hello,
I’m a new Figma user and I’m struggling to learn. I’ve created my frame and have created a component which is my bottom tab for my mobile app. I am trying to apply the fixed position in the constraints part but it’s not working. I have already made my frame scrollable and I have tried to create a box and apply the fixed position constraint on it however it’s still not working and I am completely helpless and don’t know what to do.
How can I fix this situation? how can I make my bottom tab component fixed by constraints?