I am currently on "Step 1: Set up Fleet". The second step of that section says, "Under Fleet Server hosts, click Edit hosts and specify one or more host URLs your Elastic Agents will use to connect to Fleet Server." However, I cannot find the "Edit hosts" button.
The docs are a little out-of-date (tracked here). You can skip the step about editing the Fleet Server hosts and follow the in-product instructions instead. Under the steps for adding a Fleet Server, you'll be prompted to set the IP/host and port that agents will use to reach Fleet Server. Expand the Fleet Server Hosts drop-down and click Add new Fleet Server Hosts.
Note that the UI changes depending on context. Just look for the Fleet Server Hosts drop down.