Twitter will automatically pull the header image you've selected in your Tryst profile when you share your profile. Sometimes though, Twitter is slow to update to a change you've made and you may need to force it manually.
To force Twitter to update the image it uses for the share card, head over to https://cards-dev.twitter.com/validator and paste your Tryst profile link in the profile box and click Preview card. You should hopefully see an updated preview of your share card with your new image.
We also don't send photos to Twitter that include nudity to avoid your account being flagged by their moderation team. We know it sucks, we hate it too, you can read more about how we apply our photos guidelines to get a better idea about how they affect your profile.Tryst's photo guidelines