I'm doing the quest "Weapon of the Jedi" Part: Investigate the forge entrance, I investigate the whole thing, defeat Bengal Moor, and when I'm about to turn the quest in it says "you have to have T7-01 with you" or something. The problem is, he is not there because he did not follow me from the start of the quest. He is not yet my companion so I can't summon him. What can I do?
This appears to be working for people who obtained a "temporary" companion after Patch 4.0 (open the Companions and Contacts window to summon them), but is broken for people who had a temp companion before the patch; see this Reddit post.
(For clarity, in pre-4.0 content most companions temporarily accompany you during critical quests before becoming "permanent" companions; it's this temporary state that was not properly migrated into the new system.)
At this point, all you can do is wait for it to be fixed — or, since you are on the starter planet, you might opt to delete the character and start over.