I have two sound core motion pluses one has a firmware of 7.3 the other one is four point something

I have two sound core motion pluses one of the firm wears is updated 7.3 and I have another one I bought earlier last year and the firmware ain’t even 5.0 I cannot link the first one that I bought last year I just bought another one a couple of weeks ago I cannot link them together for no having problems think it’s the firmware on the first one I bought and someone help