When I click on freelancer profile from chat, I see Hire now button, but I've already hired this freelancer and want to add a new milestone.
Where is the quick link to create a new milestone from the chat for the existing freelancer?
on the chat you go on the upper right corner with the 3 little dots icon, then it drops down and selects view contract. In the contract go under milestones and you should be able to add them there.
You can also go jobs>all contracts>find the correct contract>add milestones