You should be able to just specify the variable name PATH in the user vars, and separate the values by semicolons
; and it should pick it up after you restart the computer. If it doesn't, you can try to restore the path variable the proper way.
The reason you're seeing the unexpected dialog is because the original/official PATH var was deleted and Windows just things you're adding adding a custom variable. Go ahead and add several directories to the PATH var and restart. It should detect it and act as expected, but.... If you just installed Windows fresh, I recommend reinstalling again because if the PATH var is mising, who knows what else may be wrong.