If the mapping fields did not populate while creating a campaign, you can try the following method to troubleshoot the issue.
Go to LeadsTunnel's settings and update the Facebook token.
Go to the campaign and select the Facebook page. Then, update the Facebook Lead Form by clicking on the "Update Facebook Form" button.
If the above methods still doesn't work, please do send us a tech support ticket at firstname.lastname@example.org for further assistance.