Appliqué experts - advice needed please

[RockingMyFiftiesNot]

Don't want to post photos as fairly outing.
I bought some curtains which really match the colour scheme for our spare room . They are a bold pattern, lots of oval shapes in different colours. They are almost perfect but one of the shapes is a blue colour which I really don't like and is starting to put me off otherwise lovely curtains. I was wondering about buying some material which tones with the rest of the curtains and sewing over the shape I don't like. I guess this is appliqué? But I'm not quite sure how to prepare the shapes before sewing on (appliqué novice if you haven't guessed!) Do I cut out and hem the shapes to stop them fraying? If so how do I do that with rounded shapes? Or if I cut out and sew on will they not fray?
I know I could sell the curtains and start again, but if I could cover the few shapes that are annoying me, they'd be perfect. Any advice appreciated, thank you

You can buy adhesive backing that you iron on. The easiest way is to iron it into the back of the replacement fabric, but out the shape you need them iron it on to the curtains. Here is a video showing how it works m.youtube.com/watch?v=BwcaC2dnuLo

You can use something like Bondaweb - it's papery with glue on one side. Place the gluey side onto the back of the fabric you want to cut out and then iron until it sticks. Cut out the shapes (with the paper still attached) then peel the paper bit off - it should separate from the glue, if not then iron it a bit more. Then place gluey side down onto the curtains wherever you want and iron and stitch on top to secure it properly. It really helps with both the fraying issue and also it doesn't move around when you are sewing!

Great thank you

Or you can do needle turn appliqué to get a smooth hemmed edge finish. It’s a bit of a fiddle to do though…

Thank you for all the advice. I've decided it's a bit of a big job for a novice so will see if I can learn to live with the curtains as they are. I showed a friend who really liked them and thought I'd be crazy to try to change them. So I'll leave for now and maybe practise appliqué techniques meanwhile. Thanks again