How to make my horse more bendy!?

hi i have a ex racer and when i got her she hadnt been ridden for 6 months and was very stiff just got her lunging on ground first and then i starting riding her and just be doing loads of circles it all takes time there is no fast way of doing things the muscles need to be worked up slowly and if you try and rush thing you could do more harm then good it could take anything upto a few month to loosen him up how long have you had him ? how old is he ?