Create a safe space for each cat, with their own litter box, food and water bowls, and toys.
Start by swapping the cats' bedding so they can get used to each other's smells.
Once the cats are comfortable with each other's scents, you can allow them to see each other through a closed door or baby gate.
Once the cats are comfortable seeing each other, you can start supervised interactions in a neutral area of your home.
Reward the cats for positive interactions with treats and praise.
If you're struggling to introduce your cats, you may want to consult with a professional animal behaviorist.
There is no one-size-fits-all approach to introducing cats. Be flexible and adapt your approach to the individual cats involved.