Hi FellowshipUMCmedia,
I understand you are unable to open AVCHD files in QuickTime.
As stated here: Using AVCHD files with QuickTime Player, QuickTime does support AVCHD files.
Therefore, I would recommend ensuring your Mac is up to date. You can learn how to do so here: How to update the software on your Mac.
It may also be worth re-importing the files incase any issue occurred during the previous import.
Hope this helps! Feel free to write back if you require further assistance.
Thank you for using Apple Support Communities.
Cheers!