Can I get the return for the tuition and other expenses? I got the AOC 1 time before. I got undergraduate degree in 2018, since September 2019 I am in a graduate program.

Tuition and fees deduction reduces your taxable income, so it may reduce the amount of tax you pay, but it is not a refundable credit like the American Opportunity Credit.

 The American Opportunity Credit (AOC) can not be used for graduate school, even though you did not use it your full 4 times.  You say you used it once.  But, you parents probably used it the other 3 times.  If not, you (or they) may want to look at filing amended returns for past years, to claim it.

The deduction and credit available for grad school education, is non-refundable.  That is, it can only be used to reduce an actual tax liability.  If your income is so low, that you don't qualify for a credit, maybe it's low enough that you parents can still claim you as a dependent (and claim the credit/deduction on their return).