That’s not really how the system on Stackoverflow works. You can give a bounty to any answer not just the one you accepted.
It’s also not lost but:
If you do not award your bounty within 7 days (plus the grace period), the highest voted answer created after the bounty started with a minimum score of 2 will be awarded half the bounty amount (or the full amount, if the answer is also accepted). If two or more eligible answers have the same score (their scores are tied), the oldest answer is chosen. If there’s no answer meeting those criteria, no bounty is awarded to anyone.
That’s not really how the system on Stackoverflow works. You can give a bounty to any answer not just the one you accepted.
It’s also not lost but: