You cannot access the charm unless you paid for the game, the free trial will not unlock it.

If you haven't already, link your Steam account to your Behavior account at the Behavior Account Website[account.bhvr.com]
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While logged into your Behavior Account click the tile under the Your Games section for Dead by Daylight:
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Underneath the Cross Progression section you should see the rewards you're eligible for, including the Trapper Charm from Flippin Misfits:

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Copy the code and redeem it like you would any other code in the Dead by Daylight shop. You should now have the charm on both survivor and killer.