Your profile is a small, personal touch: a photo and a name that show up in Tradish. You can change either one whenever you like on the Edit Profile screen. Open it from your profile, under Account, by tapping Edit profile.
Tap the avatar at the top of the screen to set a photo.
The photo comes straight from your phone's library, so choose whatever feels like you.
Under Name, type what you want shown on your profile. You can use up to 40 characters, so a first name, a full name, or a nickname all work. Leaving it blank is fine too.
When something has changed, the Save button becomes active. Tap it to keep your edits. If you have not changed anything, Save stays greyed out, which is just Tradish telling you there is nothing new to store.
That is the whole screen. Two things, a photo and a name, and one button to save them.