If you meet the following (mainly Paragon Mass Effect 2) conditions, AND have four bars of Reputation, then you can choose the Paragon (blue) option in the dialogue and resolve the Geth/Quarian conflict peacefully.
Have both Tali and Legion alive from an imported Mass Effect 2 save. Prevented Tali’s Exile in Mass Effect 2 Resolved the Tali/Legion conflict in Mass Effect 2 Completed Rannoch: Geth Fighter Squadrons Completed Rannoch: Admiral Koris, and saved Admiral Koris First side with Tali. When Legion pleads with you to reconsider, you will have both a Paragon and Renegade option. Picking Paragon will restore peace between the two sides. You can also side with Legion first and tell him to upload the code. When Tali says that the quarian will be wiped out, the same Paragon and Renegade options will appear. Pick Paragon for peace.
How can I edit the save so I can meet these conditions? I have read that you can use Gibbed.MassEffect3.SaveEdit to edit ME save files.