Sleep training?

My LO is almost 8 months, she sleeps perfectly at night, I mean she does wake up 1-2 times but I don’t mind it. I’ve always rocked her to sleep and don’t judge me but due to personal/medical reasons I’m having problems so I can’t do that anymore and would like to know a way to get her to fall asleep without me rocking her. I tried once putting her in her crib and went outside the door but she started to cry as soon as I went out so I immediately picked her up, crying is not an option. I also placed her on her crib & sat down next to her but she would just smile,tries to play with me even tho I don’t, obviously I want her to sleep so then she starts to play and talk to herself. I sat there for 1 hr and she never went to sleep until I picked her up and rocked her she was out within 5 mins so she was sleepy. Help please!!