As a general rule, any request for a modification of the custodial arrangement must be based on some substantial change in circumstances. If you are stating that the other parent now works 12 hour shifts and is therefore unable to properly care for the child, then this might constitute a substantial change in circumstances.
If so, you would need to file a petition with the family court requesting a modification. While it would be preferable to retain an attorney, you might consider handling the issue on your own. If so, you could begin by going to your local clerk of court. The clerk should have template documents that you could use for this purpose. Simply tell the clerk that you are interested in modifying your custodial arrangement and they can provide you with the appropriate documents.
Please let me know if you require any clarification.
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