Is there any way that I can prevent keloid after microblading?

Sometimes the full scar needs to be surgically revised; this entails surgically cutting, removing and restitching the scar with or without radiation or steroid injections/5fu. I recommend getting a formal evaluation with a cosmetic dermatologist/plastic surgeon to determine if that's the best option for you.
Pigmentation can be treated using Cosmelan peel or lightening creams such as hydroquinone, kojic acid, and retinol. Non-ablative lasers like Fraxel combined with vascular lasers such as excel V, Yellow laser, VBeam/Pulsed Dye Laser, and Venus Versa IPL can help if you want to try and avoid surgery. Microneedling/PRP is recommended in combination with lasers and skin care to help with color, texture and tone. Please see an expert. Best, Dr. Emer.