Robin, about 40 years ago I found a Hugh Tracey Kalimba in a music shop in Melbourne (while we were over the ditch on holiday). (Did you see the stage show, "Wait a minum" when it came to this part of the world?)
There were 2 types/scales available, one starting with doh as the longest one, the other starting halfway up the scale. I chose the Alto that gave a 2 octave scale from G to G.
I think the other was Treble and I'm not sure if it started from C or D but was still in the key of G. Just read the booklet (still in mint condition) - the Treble has 17 keys from low B to top D.
So to tune yours, with only 7 notes, you probably want:
L to R: E,C,A,G,B,D,F#
Hold it in both hands, thumbs on top. Hit the longest key (G) with your right thumb, then the next (A) with the left thumb, B with the right, C with the left, D with the right, E with the left and F# with the right.
Or tune it to any scale you fancy but the idea is the same - the longest in the middle and sloping up each side to the highest notes, with the notes alternating from side to side.

Robyn