Sleep training in the middle of the night

My baby is 8 months old and since the 4 month regression has been a terrible sleeper. We haven’t had one night since where she’s slept more than 4 hours. We have the bedtime routine perfect and she goes down to sleep with no issues about 7:30/8pm but staying asleep is the issue. We were up maybe 10 times with her last night with an hour long wake in the middle where I changed her nappy and gave her nurofen. We are exhausted. How do we sleep train in the early morning hours. She’s in her own room now. It’s so hard to know what to do. We have neighbours attached to us so can’t leave her crying for too long time (not that I would ever do this anyway tbh). I’m at my wits end and just so done. I’m also going back to work next week so will need something to change!!