As far as I know, you cannot set the avatar of a player without having teams enabled, but if you DO have teams enabled. This is how you set the avatar:
Create a team, with the same color as the "Team Spawn Point"
In that team, you should see something like this

(Click the "Full" button to get the dropdown)
Full = Full body suite, except for face on the avatar: EX, it would look like this if the team color was red.

Shirt = Only the color of the shirt would change EX:

(Everything but the shirt is my avatar)
Custom = You set what you want the team's avatar. EX: You would click "Uniform" and whatever you set that to, will be the entire team's avatar. (This does not depend on the team color, you can change it to anything)
NONE = The players avatar will stay as is without being changed. EX:

I hope this was helpful, if not. PM me.