I rolled over my entire 401k after I retired. I received form 1099-R. Box 1 and box 5 have amounts. Box 7 has the letter "G". Where do I enter the amounts on form 1040?

the code G is a direct trustee to trustee, rollover. You do not pay any tax on it. The gross distribution will be include on Form 1040 line 16a as rollover but nothing will be added to line 16b, which is the taxable amount
Since it not taxable, leaving it off will not effect the refurnd/tax due on your 2015 return, but it does not follow the paper trail.