Yes, according to IRS 2019 Publication Health Savings Accounts and Other Tax-Favored Health Plans, page 8, you can make contributions to your HSA for 2019 until April 15, 2020.
See pages 2-11 for more details on Health Savings Accounts.
Hey @KathrynG3 thanks for responding to my question. All my 2020 contributions are showing up in my 2020 1099- SA. My 2019 1099-SA is blank since I had a FSA in 2019 which is closed now. The Health Equity agent said that I can’t make any 2020 contributions to my HSA to count towards reducing my 2019 taxable income. Is that accurate?
"All my 2020 contributions are showing up in my 2020 1099- SA. " - that can't be right - the 1099-SA reports on distribution (money you spent), not contributions. But if you spend as much money as you put in, it may seem like the 1099-SA shows contributions.
"The Health Equity agent said that I can’t make any 2020 contributions to my HSA to count towards reducing my 2019 taxable income. Is that accurate? " - yes. You can't contribute to 2019's HSA if you were not eligible to do so because you had a Health FSA at the same time.