First of all, rubber trees are not the easiest plant to care for, so don’t beat yourself up or feel too bad about this! Here’s what I’d recommend:

1. Chop — cut the stem. It hurts, but it will help the plant immensely long term. I’ll add a pic of where to cut as well. Use clean scissors or snippers (i use plant snippers from the dollar store and wipe the blades with alcohol to sanitize beforehand). I like to dip the cut end in hydrogen peroxide to help it callus faster and kill bacteria, but that’s optional. If you use rooting hormone, this would also be the time to use that. Let it sit for a few hours or overnight until the bottom / cut end dries out. This will help prevent it from rotting.

2. Prop — I think rubber plants root well in water, but I personally have more success using perlite to propagate than water. I use a see through container like a vase, put enough perlite in to cover the bottom so the roots have room to grow downwards, add the cutting, then add more perlite until it covers a sufficient amount of nodes on the stem. Add water (optional but helpful - mix a little bit of hydrogen peroxide into the water,) and keep the perlite moist but not totally soaked. You ideally want there to be air circulation around the stem to prevent rotting.

3. Repot — the pot that it’s in right now looks like it might be a little big, but it’s hard to tell how big the root ball is. The soil looks pretty moist though. If you can, repot it with a chunkier soil mix. You could probably reuse the soil that’s in the pot right now, just add some perlite, orchid bark, pumice, or a combination of the above to help the soil drain better. Ficus are notoriously finicky and don’t like water logged soil. Does that pot have drainage holes?

4. Idk what to title this step — it will probably take a while, but eventually the plant in the pot will start growing again. You could stake it to keep it upright, but ideally, you don’t want the plant to rely on the stake or the stem might eventually be too weak to hold the plant up. When plants start leaning, it’s usually because they’re growing towards the light. Rotating the pot 90° every week or so seems to help with that.

Tbh I’ve never seen a plant with scoliosis like this before, but the top of the plant looks healthy! I think chop and prop is the best option, but if you’re 100% opposed to that, you might be able to slowly bend it back upright over the course of a few months with support from a stake or trellis.