Can I claim Tax Relief for Course Relief Fees that should've been claimed 1 year ago?

Yes, it is possible but you have to meet certain conditions set out by IRAS. From the IRAS website:

Deferring Course Fee Relief Claims

"Your assessable income is $22,000 or below throughout the duration of the course, seminar or conference that leads to an approved academic, professional or vocational qualification and claim the relief:

1. In the first Year of Assessment when your assessable income exceeds $22,000; or

2. Within 2-YA period from the YA relating to the year you have completed the course or attended the seminar or conference, whichever is earlier."

Look under 'Deffering Course Fee Relief Claims' and the examples provided from this page: https://www.iras.gov.sg/IRASHome/Individuals/Lo...​​​