The Check light basically applies to an LP gas mode failure, normally an attempt to light the burner that failed.
Turn the fridge off as Donn advised to see if that clears the check light. If it does, LP Gas mode should work after. Make sure the main valve at the LP tank is turned on before attempting to use gas mode. If the Check light does not clear, there may be a problem with the control circuit board in the fridge. If the Check light has stayed on, something is wrong and that will inhibit LP gas mode operation.
Please give the fridge model number, e.g. RM2852, in your reply, so that we know how to answer better. There are about a dozen Dometic brand fridges currently available, plus many more over the last 25 or so years.