If it’s just a matter of the waist sliding off your hips, you can usually turn the skirt inside out, make a triangle with the excess waistline being one side and the opposite point being the hem, and then sew the crease like that. If you have details you would like to keep centered, do it twice, one on each side, with half the excess instead. I’d probably do this at the sides, where your hips would be.
Once that’s done, you can decide if you want to remove the triangles or not. If you don’t, you’ll have the option of letting it out again at a later date if necessary, but you’ll have those bits of fabric on the inside to deal with.
If the skirt is pleated, you can skip the triangle step and just sew the waistline excess together.
The hardest part of sewing is the part I told you: figuring out where to sew and why. Second hardest is getting the thread in the needle.
Your first sewing lines will look like crap, and that’s okay, because they’re on the inside where nobody can see them. That’s why we turned the skirt inside out first. =)
Oh, and if you want to lean into the jank, you can use a stapler instead. Does the exact same thing as sewing.