If one has no sharping levers on your harp, does that mean one is stuck with mainly the C-Major Scale for the rest of the life of the harp? No!
There are alternative tunings for fixed, C-Major harps. If you've (or, your harp maker) created a strong harp, there are several keys we can tune our harps to.
Yes, it is not an instantly quick process done on the fly while playing your harp. Yet, different keys (tuning) does offer a change of pace for what may have become stale for you & your music. A change of key for a week, month, or large part of a year can provide us with a new sense of adventure & musical creativity beyond any possible ruts our fixed-key harp may have gotten us into.
While some folks are just fine with the literally thousands of songs that can easily be played on C-Major, providing a lifetime of enjoyment, some of us who don't have a harp with sharping levers may want more musical adventures! Besides the typical C-Major Scale of my own harps, I've tuned my great harp to E-flat in the past, including D Major. What a lovely sound!
I suspect it would be best to stay with your stock, C-Major Scale your harp came with for teaching & learning. It will be a lot easier on your harp teachers or children to stay with the familiar, standard tuning. Yet, once you've made progress on learning your harp or are already well-seasoned, a change in tuning could be attempted.
First, it is your responsibility to know if your harp can handle adding several sharp notes to it. Sharping notes on a harp slightly increases the string pressure on the harp's superstructure. And, that is OK for most harps can handle this. Typically, one doesn't lift all the sharping levers anyway, making any added tension minimal.
When changing the harp to a flat scale reduces tension slightly or if a mixture of sharps and flats, an overall increase in pressure is negated.
For instance, consider an E-flat scale, E, A & B-flat. Simply de-tune the harp a half step down for each of these notes, using your e-Tuner, of course.
Or, go for the keys of G or D by adding C &/or F-sharps. Simply tighten those particular strings a half-step high, the same as a sharping lever would do if installed on your harp.
One might even be able to go up to the Key of A. Or, down to F or B-flat.
To help us do this, a little study of scales, modes, chords, keys, etc. could help us who are uncertain or have little musical experience before getting our harps. I have found it helpful, and my various music teachers have recommended a chord wheel throughout the years.
While I have no affiliation with this organization, Hal Leonard books made one by Jim Fleser called, The Chord Wheel. Look it up at your favorite music or book store or Internet site. It is a short book, including a movable chord wheel on the front cover showing the mechanics of musical keys & chords, etc., and how to achieve them, etc. It is a precious resource for any musician at any level.
So, if you feel your harp is up to it, give a key or Scale change a try.
(The associated blog picture is taken from the public domain & remains the owner's copyright.)