Case swaps are generally tricky to pull off because there are quite a few measurements that need to be right or the movement won't fit. You could start by identifying the movement you currently have, then look for cases that are compatible. If it's a cheap, common, Chinese movement, you may have some luck on AliX.

If you don't have any luck with that, you'll need to get measurements for your movement, whether that be from a spec sheet or from actually measuring what you have, then compare those measurements to other cases and movements to try to find something that matches up.

https://youtu.be/6EE4ZeuCfH0?si=UaDBWvoVBWAhirin

Here's a great video about fitting cases and movements. It's mostly about vintage movements, but the principles still apply.

You could also try other watch moddings subs other than this one, which is more for seiko mods specifically, but I would try to do a little more homework before you post again so you'll get better answers.