I mint this picture on opensea as NFT, which I drew on the phone years ago. But I don't know how to promote it.
Simply use the traditional methods of marketing like share it frequently in social media and talk about it to your closed who might help you promote it. Bitcointalk is a great platform to promote your product, so don't hesitate to talk about it here and there (without spamming).
I don't know which network you used to mint your NFT as you don't provide much info about it, but if you didn't use Polygon amatic network, you can add your NFT to other marketplaces. Yes i know Polygon is much more cheaper, but it's only available on OpenSea and you can't offer it for sale in other Markets.
I have tried to figure out what this picture represents exactly. Sorry to tell you that all what i can see (No offense) is a really bad cover of the famous paint 'The scream' Edvard Munch. Who you think will be interested in it?