Hi ,
Thanks for reaching out to Activation-Dynamic Tag Management forum . We offer sincere apology for the delay in response.
As per the above scenario, you can create a Rule ( Event or Page Load based on the requirement) and then add the Facebook pixel code as an Sequential / Non Sequential Javascript / Html code under Javascript / Third Party Tags tab in a rule . Please refer the following link for more details on Third Party tags and rules.
https://marketing.adobe.com/resources/help/en_US/dtm/t_third_party_tags.html
https://marketing.adobe.com/resources/help/en_US/dtm/rules_page.html
https://marketing.adobe.com/resources/help/en_US/dtm/rules.html
Please do let us know if you have any questions or queries.
Thanks & Regards
Parit Mittal