There are tons of online PMHNP programs (which I assume is what you meant). Literally hundreds. Fewer have PMHNP than FNP but still many.
To start, look at local universities where you live and see if they have an online program. It's good to go to a known program local to your area that also has a in-person BSN program: It will make it easier to find a job because of connections and because it will be a known school to employers. Look at their GPA and other requirements. If your cumulative GPA is higher than 3.5 you should be good almost anywhere. If you're over 3.0 you'll have options but may need to apply to more schools
Talk to NPs where you live (even those that aren't PMHNP) and ask them where they went to school.
If there are none local to you, then you'll need to search wider. It's hard to know where to suggest without knowing where you live. If you live in Seattle then Seattle U or Gonzaga are good choices. If you're in North Carolina, UNC would be good.
The other things to consider are: Accreditation. Whether or not the school finds preceptors or if you have to find them yourself - a big problem for some students. Cost. Time to complete. If a GRE is needed to apply. Whether or not some in-person sessions are required.