apparently there is a security alert with my account, but i can't link my account to hypixel.net to fix it

i don't know what affects versions or components is, i put random things there. my system is minecraft java, release 1.15.2. i can't get into the hypixel servers beause im apparently banned due to a security alert in my account. i tried to go to hypixel.net to fix it, but i need to link my account to continue. i typed /linkaccount in the game like it told me to, but instead of showing me a link, it said "command not recognized." so now i don't know what is going on, or what to do.