A lot of horror writers submit to anthologies. Keep an eye out for calls for submissions on social media groups or forums dedicated to horror writing. Another option is to approach indie publishers who have a focus on the horror genre. Just make sure to follow their submission requirements precisely.
Some publishing houses specializing in horror fiction also accept submissions. For example, 'Blood Moon Press' has open submission periods. Check their official websites for details. Also, there are online writing communities like 'Fright Writers' where you can share and potentially get noticed by publishers or editors.
You can try submitting to well-known horror-themed literary magazines or websites like 'Horror World' or 'Dark Tales'. They often have submission guidelines on their platforms.