How to Create a Filter To Identify First 3 Text Characters - In Power Query

I have a database with millions of records. Each record is identified by a number and text description. Therefore, I want to create a lookup by the first 3 text characters that begin with "EDT" and rename it as "External" and if it does not begin with "EDT" then call it "Internal". 

Example:

ELM-HEMLOCK 1.6MI 1PH RBLD PITA1328 - This should return "Internal"

EDT:  OREILLY RD BRODERICK RD 1.7MI 1PH OH RBLD WINNECONNE - This should return "External"

Thanks in advance.