*Dim 7 chord originates from a dominant 7chord by simply flatening your second , third and fourth fingers asemi note backwards.
Here the trick is the diminished 7 is made up of four notes so by inverting the first route chord three times, u cover diminished chords of the other three notes.
Lets take a look at this
➡ C Diminished 7 is made up of notes C , Eb, Gb, A
* when you invert it its first inversion gives you Eb
Diminished 7
* Inverting it second time gives you Diminished Gb
*Third inversion gives you A diminished 7
~ with only C we have covered diminished 7 chords for three keys
➡ D diminished 7 is made up of notes D,F,Ab,B
* First inversion gives u F dim 7
*second inversion gives u Ab diminished 7
*third inversion gives u B dim 7
~here we have covered more four keys
➡ C# dim 7 is made up of ( C#,E,G,Bb)
* first inversion gives you E dim 7
* Second inversion gives you G dim7
*Third inversion gives u Bb dim 7
*NB. summing them we have diminished 7 chords for all 12 keys
#@jpro keys simply all 12 keys by observation