My son transferred from D3 to D2 in a different sport - did not have to sit a year.
First thing he did was contact the NCAA.
Then he contacted the NCAA compliance officer at the D3.
The he talked to the D3coach - was up front as to why he wanted to transfer. (it was NOT sports related)
Had to get D3 schools permission to allow D2 schools to talk to him.
Once he picked his school worked out the necessary paperwork and NCAA notifications through both the D2 and D3 compliance officers.
We (the parents) were not involved except to guide him with the questions to ask, advised him to make sure all communication and in writing and copies kept.
He was 18 - 19 at the time - a man - he was the one responsible for the decision and the consequences of any missteps. Came through it with flying colors. Other than visiting the school he finally picked, we had no communication with the coach, AD, or anyone else in the program before his decision and minimal interaction since then. And that has been just pleasant conversation at an event.