You can go ahead and enter the one you have but do NOT e-file. Your information will be saved until you come back to the account and enter your other information when the other W-2 's arrive.
Every 2019 W-2 that you received must be reported on your 2019 tax return, even if they are for small amounts. Remember that each one of those W-2’s has your Social Security number on it, and that income was reported to the IRS by the employer. You do not want to get in trouble with the IRS for under-reporting your income.
ALL of your W-2’s must be entered on the SAME tax return. After you enter the first one, you click Add Another W-2.
W-2's come from your employer, and they have until Jan. 31 to issue it. Some employers allow you to import the W-2 through the software, but often you still need information from the actual W-2 just to import it. So waiting for your employer might be your only choice now.
When you first go to the W-2 topic, is it showing you an employer that transferred in from last year? Is there no option to skip that particular W-2 for now? For instance, is there a button somewhere below it that says "Add another W-2"? If that button is there, then go ahead and click to add the W-2 that you DO have. Later after you receive it, you can go back and provide the info on the W-2 you haven't received yet.
If there's no way to get by it, another possibility would be to skip through the screens for that unreceived W-2, and at the end of that W-2, you can click on "Add another W-2" to enter the other W-2 that you DO have. Then later when you do get that W-2 you skipped through, you can then go back to the W-2 section and choose "EDIT" by the skipped job to provide the info.
And, of course, as xmasbaby0 cautioned above, do NOT efile anything until you have ALL of your information entered and finish your return.