Getting rid of a mold spot on drywall

If you are really worried about it spray Concrobium on it then kilz and then paint.

The drywall is already damaged, you are now trying to cover up the damage.

If the mold is still active, then that needs to be addressed.

If the Kilz does not sufficiently cover the stain, the try old fashioned hairspray. That seems to work better than KIlz for stubborn stains.

I used bleach solution in a spray bottle (just wipe it up and put a towel down to protect carpet) and a dehumidifier, repeated process after a couple days while running dehumidifier constantly, then painted over it with kilz drywall primer then painted. It was only outside the dry wall though.

If it’s inside, replace the drywall.

ETA:

Get a moisture meter, not too expensive. It'll tell you if it's actually dry. If it is, just use a bleach solution and paint over it.

If the cause of the "mold" was fixed, then most likely the "mold" is no longer an issue. If the problem was never identified and corrected, then that "mold" spot is not your only issue.

The only way to know for sure is to cut out the affected area and repair it.

Is there a way to see the back side of the drywall?

Kilz in the white can should do. If not, then Pro Block from Sherwin Williams will.

If you haven’t opened it I would try to return that. Get the white spray can, spray lightly each pass rather than blobbing it on there and have it run.
Think mister, not firehose. Keep the can moving.