Negotiation

Hello I'm expecting to get an offer from a company initially I asked for $90,000 first HR said should be fine and then got back to me saying. Really the position can only pay $80,000 so I accepted it. I wanted to continue with interview process. After the interview finished it's been awhile and now they told me they are in the process of deciding about the salary. I am hoping to hear back from them soon. My question is how can I negotiate with an offer I agreed in the beginning of the interview process TC 79 2yoe