You can add eligible expenses you paid that are not included in Box 1 of Form 1098-T. IRS states that the amount shown on Form 1098-T may differ from the amount you paid. Here’s relevant information from page 20 of IRS Publication 970.
Form 1098-T. To help you figure your American opportunity credit, the student may receive Form 1098-T, Tuition Statement. Generally, an eligible educational institution (such as a college or university) must send Form 1098-T (or acceptable substitute) to each enrolled student by February 1, 2021 (January 31 falls on a Sunday). An institution will report payments received (box 1) for qualified education expenses. However, the amount on Form 1098-T might be different from what you paid. When figuring the credit, use only the amounts you paid or are deemed to have paid in 2020 for qualified education expenses.