I have a horse with a horrible mane 😂 It goes forward towards her ears. I found that by washing the mane and then sectioning it out into 15cm and then braiding down halfway. I then put a Lycra hood on for the first day to encourage the mane to stay down. After a few days I take them out give it a wash and go again.
Hope this helps
I groom my horse everyday and as he is a Dartmoor and we let him have along mane I struggle with this but what I found helps is combing it over everyday from the roots.
I usually make a lot of little braids and leave them for a couple of days at a time, eventually it trains it over but It reverts back.
At the moment (I have the same problem) I just make little ponytails to the side where I want the mane to stay, because it is not as uncomfortable as braids 😊
If you have a slinky hood you can use that a few times and it should help a bit.
Braid the mane to the side you want it to be on tightly overnight every few days. (Doing it when their mane is wet will help it even more!) Then eventually it will stay to that side.
braid on one side several times