So that little bar never worked for me, but I just revisited the education page and looked at the relevant educations and now it does, maybe that helps
There's normally three possibilities for overclocking to be blocked if you already have the edu - You have insufficient power: Overclocking increases power consumption for all components except fans linearly, and you cannot overclock unless you have power to spare. Adding one or more PSUs for additional power may help. - Extensions may be causing issues: It's a known issue where some extensions like torntools can block overclocking in some browsers. Try to disable them and check again, see if it remains blocked. - Its a mere visual bug: Sometimes, usually after messing with the rig, it'll bug out and overclocking will be blocked. Just empty your rig, reload the page or reopen your browser, and try again.
Posting a picture of your rig would be the easiest way to confirm whether overclocking should be possible for you.