ABAQUS subroutine UEXTERNALDB

Hi, I'm new user of ABAQUS. I'm trying to develop a model that involve one further output variable (the degree of cure of a polymer). I thought to use the subroutine UEXTERNALDB to write and read from an external file the array containing the values of this output variable in each element. But I couldn’t find out how to call this subroutine in the .inp file. Does anyone have any suggestion for my problem?

Thank you