How do i get my admin account back?

Last year i had been in a school called International School of dongguan where i had to bring in my own laptop to school, they set up an administrator account and removed mine in the middle of the school year. It hadn't been a problem since now because for some reason a bug on my Macbook set the time to March 31st and I couldn't change it.

I asked my tech teacher how to fix it and he told me the password and told me to log into the Admin account however it showed that the account is locked. I did not know what it meant and how to fix it.

Now since the time is set in the future, almost all my apps stopped working, can anybody help me either change the time or get my admin account back.