You need a lameness/soundness evaluation from a vet to best advise you
That is not a mildly crooked knee
Not something that would be caused by 1 poor trim.Was his leg correct/straight before?? Surprised he is not lame...
Corrective trimming is not going to correct a deviation such as that at his age
not great pic but from what can see To me ,This horse looks like either he sustained an injury or that that leg was never very correct in first place & then maybe a poor trim job aggravated it to have it look worse.He didn't suddenly go crooked like that from one trim