Is there a link on the Scoutbook website to assign myself as a merit badge counselor for a merit badge?
It depends on what exactly you are trying to do.
If you are trying to register as a merit badge counselor for a merit badge, (all merit badge counselors must be registered and approved for the particular badge they wish to council,) then contact your local council service center for assistance.
If you are already registered, the Scoutmaster of the unit can invite you to counsel a Scout by following the information here:
More information is available at our help center here: http://help.scoutbook.com