Well, do you think that they'll accept? If so, you can start wearing things like bracelets that have the colors of the non-binary flag. Or, when it's a good moment when they aren't angry/sad or busy, could say "I think I'm not [insert previous gender here] anymore." Or, if they call you he/she, you could say "can you please call me they/them". Or, if they deadname you and you already have found a new name for yourself, you would say "can you please call me [insert new name here]?". Anyways, whatever way you choose, you're valid!