VSWR Meter dB scale Vs. SWR Scale

In the figure shown below, SWR Meter is using in two different
scenarios. First one for SWR measurement and second one for
dB measurement.

In SWR meter, same needle rolls on two scales simultaneously.
There is no any front panel controls to switch between dB and
SWR scales.

Then how can I confirm the first setup is for SWR and second
is for dB ?

In short, my doubt is that-Whether it indicates input VSWR or
feeding power of Horn antenna in the first case on SWR Meter ?

The diagram on the left shows the connections for deriving v.s.w.r. You have to make two measurements with the slotted line. One of the highest and one of the lowest voltage.

Not knowing what make and model your voltmeter is, it's impossible to say how it reads v.s.w.r. The manual will tell you.

your questions and drawings are really too vague to be able to give an informative reply

how about some actual photos of the system you are using so that we cam maybe get an idea of the equip.
some makes and models would be really helpful for us guys to be able to help you


cheers
Dave