Sleep training 6 month old

Have a 6 month old girl whose sleep schedule changes daily. Nap wake windows are pretty consistent during the day, 2/2.5/3+ before bed time. She goes down around 7:45-8 every night, sometimes she sleeps until 6:30, sometimes 5:15, sometimes 3:30 and I need to give her a bottle to go back to sleep.

Just wondering if anyone has any advice on how to get a more consistent schedule