Linc23

I will be paying into a salary sacrifice pension when I start my new PAYE job, for which I will receive 40% tax relief. This will bring my actual salary down to £73,600. I have two children and currently receive child benefits. In order to not lose this I am considering using ISA savings to make a one-off payment of £13,600 into a SIPP. My understanding is the SIPP will automatically claim 20% tax relief on my behalf. I would then want to claim the additional 20% tax relief on that £13,600, which the HMRC website says can be done via self-assessment, but up to a limit of £10,000. How can I claim back tax relief on the additional £3,600, do I need to write to them separately? Also, as I am not registered for self-assessment, will I be able to register in order to claim under these circumstances?