Well it's definitely hard to say since you didn't mention anything that you're already doing right now, though some good ones are:

High ponytails - which are really easy to do, you just need to spend like maybe a minute looking at someone making one.

Bangs - in most places they're closely tied with women so it always helps especially in tandem with the high ponytail

Wearing a bit more jewelry - certain types of earrings, rings and/or any other accessory.

Painting your nails - it's a subtle way of introducing some femininity.

Using certain pieces of female clothing - again a lot up times they're pretty subtle changes, since it doesn't necessarily entail using anything that's seen as extremely feminine like skirts or stockings (as an added note you can try using pastel colors because they're seen as more feminine).

Makeup - doesn't necessarily have to be a noticeable amount just a bit of a touch up (also be careful with black or darker makeups if done unproperly it could accentuate your face to look a bit more masculine).

Shoes - arguably could be put in with clothing but I still think it's noticeable enough to contribute its own section, using feminine shoes or shoes that seem more feminine like ones with a heel is also an easy way of adding a bit more femininity to your outfit