Once your kefir grains get going, you will notice that they will start to multiply. When you get to the point of having too many, your kefir will ferment too fast. So it’s a good idea every now and then to get rid of some grains and get back to about a tablespoon of grains that you are working with.

One thing you can do is find someone who you can give some grains to and help them start making kefir too.

Here is a post that talks about some things you can do with extra kefir grains:
https://www.culturedfoodlife.com/7-ways-to-use-your-extra-kefir-grains/

If all else fails, you can throw them away. I’ve done that a time or two.