Retraining an ex barrel racing horse

Hello there! I just got an 18 year old ex barrel racing horse and it’s like she was never trained at all. She will not and refuses to stand tied and on the trail when I try getting her into a little trot she goes full speed and I can’t get her to go slower or calm down, I honestly don’t know what to do because I’m not a trainer or anything so any tips would be helpful!