The Filter area shows the frequency range currently being demodulated.
Minute adjustments can be made by clicking and dragging as follows:
It's easier to zoom in first (by right click and drag on the frequency bar). I've also increased the size of the panadapter area by left click and drag on the up/down symbol at the extreme left of the frequency bar. Either sideband extremity can be adjusted by left click and drag. A right click and drag at either edge of the filter will expand or contract the filter width uniformly on both sides of the centre frequency.
Left click and drag anywhere in the filter area (except the edges) to move the whole filter to the left or right of the tuned frequency. This is particularly useful when using very narrow filter widths. The audio tone of a CW signal, for instance, will be proportional to the distance between the filter position and the tuned frequency. Note that the filter indicator in the frequency display now shows 'USR' and the size of the lower and upper sides.