Sending in an additional Reccomendation

I’m apply to several top universities and I’m very anxious right now. I sent in 2 teacher recs + 1 counselor rec to all my CommonApp schools more than a month ago, however my research adviser (who wrote a rec for research competitions) now wants to send in an extra recommendation letter for me. Is it acceptable at this point to send in an additional recommendation? And if it is, what is the process to do so?