Creating a new companion, need some help
 

Im currently working on creating an arcane familiar / eidolon hybrid for an arcanist archtype that Im making but I cant seem to get it to work right. This is my first time working with the editor and I cant seem to figure out how to make the new type appear under "Companion Type" under "Companion Class Helper" or "New Companion Type". Is there something I need to do to link it to those lists? I already tried adding "CompAvail" as both a field and a tag but that didnt work....

You need to place a CompAvail tag on the Companion Class Helper, and then have your archetype apply the same CompAvail tag to the arcanist Class Helper at First 400.

I have the tag set for the Companion Class Helper but Im not sure what you mean when you say First 400.

First is a phase, a 400 is a priority. The phase and Priority of eval scripts determines what order they occur on a character. Add an eval script to your archetype at that phase and priority which assigns the tag to the class it is affecting. For example

First 400
Obvously, change the all caps appropriately.