Assign "Owner Field" in bionic rule from SFDC Account user lookup field - Call To Action

I'm running into issues where I cannot assign the CTA owner to the SFDC user contact from our Salesforce Account Object. 



We currently have these field below as look up contact fields in SFDC Account.

1. Account Manager

2. Customer Success Program Manager 

3. On-Boarding Manager



The CTA's I'm creating need to be assigned to one of the three above.

By default, these fields are not available for me to use as an  "owner field" 



I'm creating these rules from GS Relationship, Matrix Data, Activity Timeline, etc. for reference.



How can I get the look up contact fields from the SFDC account as the "owner field?"