Can I add overdraft to an account and reconcile account to negative balance as the client is in overdraft?

Hello sobysbookkeeping, 

Glad to have you join the Community. QuickBooks is a versatile program that enables you to get your work done faster. I'll be happy to guide you in the right direction so you can achieve your QuickBooks goals with ease. 

Recording your transactions the right way is essential for ensuring your books remain accurate. That said, I recommend consulting an accounting specialist for expert advice. This ensures your entries are recorded in a way that allows for you to navigate the program with peace of mind. You can get in touch with an accounting professional using this link here. Other accounting professionals are able to see this post in the Community and this will allow them to chime in. 

Let me know if this info helps. I'm here to steer you in the right direction.