94 Rodeo broken spark plug!

My sister called today to tell me she had her truck in at Midas for a tune up. They called her later and said they broke a plug off and it would be
about a grand since they need to take the head off. I looked at it quickly (no tools with me) but it's running on all 6 right now so they must have just stuck the broken piece back in the hole so the 2 parts of the plug are making contact. I'm not sure if the plug broke in 2 or the porcelain is cracked. If it's just cracked, what's the best way to get out a seized plug? If it broke in 2, what are my options? If I remove the valve cover, would that make for better access to the plug? TIA Rick
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