Hi Arvella-

Hope you made lots of yummy recipes with your rhubarb this season! And, how nice of you to share your bounty with friends.

The short answer to your question is: in the spring. An article from Iowa State University (see below) talks about the timing for division of the plant, replanting, and care.

Depending on the age of your rhubarb plant, I have also attached an article from Michigan State University that addresses renewal of old plants, and has some good suggestions on division of plants and rhubarb plant care.

Thank you for your question! Tenley H. Michigan State University Extension Advanced Master Gardener Volunteer
You may also contact the toll free MSU Extension lawn and garden hotline at <personal data hidden> with your gardening questions or visit www.migarden.msu.edu for Smart Gardening resources.

https://yardandgarden.extension.iastate.edu/faq/when-can-i-divide-rhubarb-plants

https://www.canr.msu.edu/news/renewing_old_rhubarb_plants