How old are the cards you have? how many inquires have you had in the past year? Just on the surface, without any other info I'd say I don't know that adding another account right now is going to help you, it may hurt you. You might want to consider staying in the garden to add age and positive payment history with what you have. Once your scores go above 670 or 680 there should be several unsecured options for an approval, and opportunity to grow. You're really not that far away if you're near the mid 600s now.
I agree with @JoeRockhead, based on the information provided, adding another card seems much more likely to hurt your scores in the short term versus helping them.
@IcyCool7227 wrote:Is it worth getting a secured card like Citi to rebuild credit if I already have a Kohls Charge and 4 other cards? What I have is Amazon Prime Store Card, Capital One SavorOne CR, SuperCash hybrid cc, and Tomo. Quite honestly would an additional card improve my score anymore or is it best to just stick to the ones I already have until something better opens up? I have scores in the near mid 600s.
No, an additional card would not improve your score in any way.
Focus on keeping your utilization below 30%, ideally below 10%, on the cards you have.
Pay balances before the statement date if necissary to do so.
