Since you only filed the Federal return, you will only amend your Federal return.
However, make sure the additional W-2 gets added to your state returns as well. You will probably need to add to Federal side so that the income will flow through to the state. It is also a good idea to wait to send your California and LA tax returns after your Federal amendment is processed since they rely on the Federal information.
Here are some instructions for amending your return:
Open this TurboTax
link and follow the instructions to add your W-2 and amend your tax return.
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
You especially need
to wait until the IRS finalizes your
original return and you receive your refund or your payment has processed.
You will mail your
return to the IRS. They do not accept electronic amendments.
The following IRS
link is very helpful in understanding the amendment process.
https://www.irs.gov/newsroom/amending-your-tax-return-ten-tips
