Range extender

I’ve recently installed Xfinity modem/router for streaming. The modem/router is approximately 50+’ from my smart tv. My tv has began constantly buffering during programming and was suggested I get a range extender due to the reduction in 5g strength at this distance. I went to Xfinity store to buy one and was told I might be able to get one free? I’m not very tech savvy at all. Any assistance would be greatly appreciated.