Copy your logo to IAM consoles war file
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Login into OIM Identity console.
Create a sand box
Provide a meaning full name and description to the sand box.
Verify that sandbox is active mode or not
Once sandbox is activated click on the customize, which is available at right side top of the window
And then click on structure
Click on Oracle Logo , and a window will be opened in the right side of the window.
select command link as shown in the screens shot and then click on edit.
After editing, click on Icon and edit again
Click on overide the expression and then provide below values in the expression
http://hostname:14000/oim/images/Logoname or file name
Save the settings and then publish the sandbox to make changes effective.