Openers rebid. Balanced
You'd got all this worked out already
If you have 15-19 HCP, or 23+ HCP, you have still not told your partner that you are balanced. So, if he has come back with an unbalanced hand, you must now tell him you are balanced and your exact strength.
If he has come back with a limit bid saying that he is balanced, you can now simply do your sums to decide if you have a safe 25 HCP and, if so, then put it into game 3NT. Or even into Slam if he's come back with 4NT and you are on maximum HCP.
The rebids for an opening balanced hand have largely been covered when considering how to open in the first place with a balanced hand, and when considering how to reply with a balanced hand, and how to reply with an unbalanced hand.
Stayman and Transfers play a large part in these responses and the rebids you must now make.
The Bidding Cribsheet - Side 1 and Side 2 also cover these points.