Ok the first thing you should do is move the betta an let the shrimp have that tank. Then go get a pc
of drift wood thats got a lot of nooks to hide in as wells as offer some cover. You also should have some form of moss or low light plant. I have christmas moss and they love it. It's also low light and doesn't require a lot of care. they also need a good veggie food. As said in other replies water quality is important. It's a 10g tank, water changes take no time at all for that size. If you do those things it should just happen. I just put 10 shrimp in a 20 tank maybe two weeks ago. I just can home from work to see I have a female fanning eggs. Hope it helps!