If there are no foster children currently living in the home, the foster carer should inform their existing fostering service of their intention to transfer to another service. This is not a resignation: that will need to be done later. Once this has been done, the new fostering service is free to commence an assessment.
Once the assessment has been completed and the recruiting service informs the foster carer that they intend to seek their approval as a foster carer through the panel and decision maker, the foster carer should then give written notice of resignation to their current service.