IRA contribution for 2019 now

I am self employed.

 

I would like to put some additional funds now, in July 2020, to the IRA account for the tax year 2019.

If I were to transfer the funds now (to maximize tax benefits), how would I designate that particular transfer is for tax year 2019? I have already contributed some funds for tax year 2020.

 

Or does it not matter?  As long as I keep track of it myself?