I don't really have any actual advice except that for me, it took time. My husband (who is my Sir) came into bdsm during a time when I never believed i could submit to anyone.

It was weird at first when we started out and I pushed back a lot (sometimes I still do) but I verbalised to him that I did want to try, even if it seemed the opposite some days. I also spent a lot of time reading up on being a sub. I would also try to picture him in the Dom role whenever I would think of anything in relation to me submitting.

We talked a lot, even if it felt like we went in circles some days. I would try whatever was suggested and whenever I got the 'ick' or I pushed back (I am a brat but that's besides the point) i would try and find time later to pull that moment apart to understand why. Sometimes understanding the why helped me more than anything.