An easy way to restore your default keybinds is by navigating to Wurst Options > Keybinds and then clicking on the "Reset Keybinds" button.
Another way to do it is to type
.binds reset in the chat.
For more info or if you want to dive deeper into customizing your keybinds, check out the Keybind Manager page on the Wurst Wiki.
Hope this helps!