Can I dye my hair if I used Sun-In, please help

Yes, but you may have to use a darker/stronger colour than you would have otherwise. Bleach like sun-in damages your hair, which makes it either more/less likely to absorb dye. Be careful with home dying after bleaching, because home dyes work with the natural pigments already in your hair, which bleaching may have removed. IE, bleach has removed the brown tones but not the orange, so dying your hair black will turn it GREEN. If in doubt, seriously, go to a salon and have a good colour person fix it. After many disasters, I have learned to do this for radical colour changes.