FICA taxes and the substantial presence test for F-1 student

I am an F-1 student and I may have just found out I passed the substantial presence test for tax year 2020. I assume that makes me subject to FICA taxes for the entire year of 2020.

 

My employer currently doesn't withhold any social security or Medicare taxes from my paychecks. If I confirm I am indeed a resident for tax purposes, how do I get this situation corrected with my employer?

 

I have not yet completed my tax return for 2020.