swipe from the left to bring up the navigation menu, and click the veeeeery top. On mine it shows my profile name but that is where it lets you add accounts.
Honestly just don't bother with mastodon.
I deleted Twitter years ago and don't miss it at all.
swipe from the left to bring up the navigation menu, and click the veeeeery top. On mine it shows my profile name but that is where it lets you add accounts.