You can go and change your default formula in Sku Grid.
Go to Settings --> Marketplaces --> eBay --> US.
Click on Use Wizard. It's recommended that you use the formula wizard to let it create the long formula for you instead of typing in a long formula because that leaves too much room for human error.
Once you've configured the formula the way you want to close out of the wizard and save the settings.
Then remove all override formulas by going to My Items --> Batch Options --> Remove Per Item Formulas.
Then Force Reprice All Items by clicking on Batch Options --> Force Reprice All Items.
Give them some time and all will be updated according to the new formula.
Videos for Reference
1. Setting Your Default Selling Formula - https://www.youtube.com/watch?v=Ym2y4y2k8PI
2. Removing Override Formulas from All items - https://www.youtube.com/watch?v=V7he_GenBiQ
3. Force Repricing All Items - https://www.youtube.com/watch?v=1zK5V3D_XGg