I am having trouble entering my QCDs. My 1099-R doesn't have line 4a.How do I get credit and tax savings for all my QCDs?

Per IRS: 

Like other IRA distributions, QCDs are reported on Line 4 of Form 1040 or Form 1040-SR. If part or all of an IRA distribution is a QCD, enter the total amount of the IRA distribution on Line 4a. This is the amount shown in Box 1 on Form 1099-R.

Then, if the full amount of the distribution is a QCD, enter 0 on Line 4b. If only part of it is a QCD, the remaining taxable portion is normally entered on Line 4b.

QCD

First of all line 4a is on your actual 1040 tax return not the 1099R.  After you enter the 1099R keep going.   One of the next screens will ask Transfer to Charity? Did you ask the Trustee to transfer all or part of this distribution of $xxx to a qualified charitable organization?

Then do NOT enter it again under Deductions & Credits.