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This is a perfect application of the nanovna.

If your nanovna has a recent version of firmware, I think 1.1 or better, it
will have a "measure" item on the top menu. Select that, and choose the
'resonance' option.
This puts a resonance display on the screen. Connect the cable stub,
leaving it open at the far end. This enables the vna to see the resonance
of that cable. The first resonance is at 1/4 wavelength, so just trim the
cable until that reads your desired frequency. Make sure to consider the
length of a connector that you will install - but that's not much of a
concern at 7MHz.

If your nanovna doesn't have that measure/resonance function, it is almost
as easy. Just connect the cable in the same way, and set one of the traces
on the vna to display S11 phase. To start, set the frequency range to
something like 50kHz to 15MHz, just to get a feel for what you will see.
With an open-ended cable attached, you will see a sawtooth pattern on the
S11 phase trace. The position where the phase first does a 'zero crossing'
from -180 to +180 (or vice versa) is the quarter wavelength resonance.
Hopefully that is happening above 7.04MHz, and you can now set the top
frequency to something like 7.5MHz, put your cursor on the desired 7.04MHz,
and trim until the zero-crossing is at your cursor. The vna should be
calibrated, of course, as always - but you can calibrate once across the
desired range, say 6-8MHz, and then change the range as noted above to help
see the zero crossing pattern.

Good Luck.
Stan