Dial *228. But if there's no tower close enough to you, or the nearest tower is blocked (my niece lives just under a ridge between her house and the only Sprint tower - I can't use Sprint in her house, but get full bars 25 feet up the block on the top of the ridge), no PRL is going to change anything.
The only time updating the PRL will help a situation like yours is if they put in a new tower (or face) and your PRL doesn't let you connect to it but the new one does.