So, when I was really young, about 20 years ago, my mom bought me this instrument from a garage sale. It's just always stuck around and I've always been curious as to what it is. I know next to nothing about instruments Haha. Any help would be greatly appreciated!

it is some kind of 15 string wooden harp or zither,it looks very basic on this photo,I guess there are no signs or letters on it on any language? maybe it is Klingon property?

Haha, ya there isn't a single word or letter on it. I honestly have no idea.

Lap harp. There is nothing written inside?

If you could download a tuner on your phone, and replace that missing string...

Start by plucking the longest string, adjust until it hits G. Then A-B-C-D-E-F#-G, repeating when you get to the high G.

Each string would be played "open" like a regular harp. There are no frets. Your chords will come from plucking/strumming multiple strings at the same time.

Lap harp, probably made in Mexico.
3 for sale on internet right now, look the same... no markings.
$20-$90

Nice lap harp