Q: I’m installing a soaking bath and wanted to add a two-handle tub filler mounted on the tub deck. But I’ve realized a two-handle filler with a spout will take up too much space for my layout ...

The tub spout you have with the knob on the end of it is a shower diverter. The knob diverts water away from the tub spout and up to the shower head. In your case, the diverter needs to be replaced.