Your profile picture can be set in your profile settings. To find the setting go to your wallet and then click Settings at the top right.
Currently Smoke.io doesn’t support uploading profile images. Yet you can easily use a (free) image hosting service like imgbb.com.
Go to imgbb.com and choose the picture you wish to use as your profile image. Upload the picture. One the image uploaded, make sure to select HTML full linked in the dropdown. You will now see the markup to insert an image.
Copy the link and select the part in between the quotes after img src=
Copy that link and insert that image link in your Smoke settings.